Add cmd_process_error() to report and process errors

U-Boot now uses errors defined in include/errno.h which are negative
integers. Commands which fail need to report the error and return 1
to indicate failure. Add this functionality in cmd_process_error().

For now this merely reports the error number. It would be possible
also to produce a helpful error message by storing the error strings
in U-Boot.

Signed-off-by: Simon Glass <sjg@chromium.org>

include/command.h

@@ -64,6 +64,15 @@ extern int var_complete(int argc, char * const argv[], char last_char, int maxv,
 extern int cmd_auto_complete(const char *const prompt, char *buf, int *np, int *colp);
 #endif
 
+/**
+ * cmd_process_error() - report and process a possible error
+ *
+ * @cmdtp: Command which caused the error
+ * @err: Error code (0 if none, -ve for error, like -EIO)
+ * @return 0 if there is not error, 1 (CMD_RET_FAILURE) if an error is found
+ */
+int cmd_process_error(cmd_tbl_t *cmdtp, int err);
+
 /*
  * Monitor Command
  *