Make sure that argv[] argument pointers are not modified.

The hush shell dynamically allocates (and re-allocates) memory for the
argument strings in the "char *argv[]" argument vector passed to
commands.  Any code that modifies these pointers will cause serious
corruption of the malloc data structures and crash U-Boot, so make
sure the compiler can check that no such modifications are being done
by changing the code into "char * const argv[]".

This modification is the result of debugging a strange crash caused
after adding a new command, which used the following argument
processing code which has been working perfectly fine in all Unix
systems since version 6 - but not so in U-Boot:

int main (int argc, char **argv)
{
	while (--argc > 0 && **++argv == '-') {
/* ====> */	while (*++*argv) {
			switch (**argv) {
			case 'd':
				debug++;
				break;
			...
			default:
				usage ();
			}
		}
	}
	...
}

The line marked "====>" will corrupt the malloc data structures and
usually cause U-Boot to crash when the next command gets executed by
the shell.  With the modification, the compiler will prevent this with
an
	error: increment of read-only location '*argv'

N.B.: The code above can be trivially rewritten like this:

	while (--argc > 0 && **++argv == '-') {
		char *arg = *argv;
		while (*++arg) {
			switch (*arg) {
			...

Signed-off-by: Wolfgang Denk <wd@denx.de>
Acked-by: Mike Frysinger <vapier@gentoo.org>

common/cmd_fat.c

@@ -33,7 +33,7 @@
 #include <fat.h>
 
 
-int do_fat_fsload (cmd_tbl_t *cmdtp, int flag, int argc, char *argv[])
+int do_fat_fsload (cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
 {
 	long size;
 	unsigned long offset;
@@ -94,7 +94,7 @@ U_BOOT_CMD(
 	"      to address 'addr' from dos filesystem"
 );
 
-int do_fat_ls (cmd_tbl_t *cmdtp, int flag, int argc, char *argv[])
+int do_fat_ls (cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
 {
 	char *filename = "/";
 	int ret;
@@ -141,7 +141,7 @@ U_BOOT_CMD(
 	"    - list files from 'dev' on 'interface' in a 'directory'"
 );
 
-int do_fat_fsinfo (cmd_tbl_t *cmdtp, int flag, int argc, char *argv[])
+int do_fat_fsinfo (cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
 {
 	int dev=0;
 	int part=1;
@@ -227,7 +227,7 @@ int find_fat_partition (void)
 }
 
 int
-do_fat_dump (cmd_tbl_t *cmdtp, bd_t *bd, int flag, int argc, char *argv[])
+do_fat_dump (cmd_tbl_t *cmdtp, bd_t *bd, int flag, int argc, char * const argv[])
 {
 	__u8 block[1024];
 	int ret;