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/image-sparse.h

@@ -33,4 +33,4 @@ static inline int is_sparse_image(void *buf)
 }
 
 void write_sparse_image(struct sparse_storage *info, const char *part_name,
-			void *data, unsigned sz, char *response_str);
+			void *data, unsigned sz);