UBI: simplify IO error codes

We do not really need 2 separate error codes for indicating bad VID
and bad EC headers (UBI_IO_BAD_EC_HDR, UBI_IO_BAD_VID_HDR), it is
enough to have only one UBI_IO_BAD_HDR return code.

This patch does not introduce any functional change, only some
code simplification.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Reviewed-by: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
Tested-by: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>

drivers/mtd/ubi/eba.c

@@ -418,7 +418,7 @@ retry:
 				 * may try to recover data. FIXME: but this is
 				 * not implemented.
 				 */
-				if (err == UBI_IO_BAD_VID_HDR) {
+				if (err == UBI_IO_BAD_HDR) {
 					ubi_warn("corrupted VID header at PEB "
 						 "%d, LEB %d:%d", pnum, vol_id,
 						 lnum);
@@ -961,7 +961,7 @@ write_error:
  */
 static int is_error_sane(int err)
 {
-	if (err == -EIO || err == -ENOMEM || err == UBI_IO_BAD_VID_HDR ||
+	if (err == -EIO || err == -ENOMEM || err == UBI_IO_BAD_HDR ||
 	    err == -ETIMEDOUT)
 		return 0;
 	return 1;