fastboot: sparse: resync common/image-sparse.c (part 2)

- update fastboot_okay() and fastboot_fail()

This file originally came from upstream code.

While retaining the storage abstraction feature, this is the second
set of the changes required to resync with the
  cmd_flash_mmc_sparse_img()
in the file
  aboot.c
from
  https://us.codeaurora.org/cgit/quic/la/kernel/lk/plain/app/aboot/aboot.c?h=LE.BR.1.2.1

Signed-off-by: Steve Rae <srae@broadcom.com>

include/fb_nand.h

@@ -6,5 +6,5 @@
  */
 
 void fb_nand_flash_write(const char *cmd, void *download_buffer,
-			 unsigned int download_bytes, char *response);
-void fb_nand_erase(const char *cmd, char *response);
+			 unsigned int download_bytes);
+void fb_nand_erase(const char *cmd);