Btrfs: do not inc uncorrectable_errors counter on ro scrubs

Currently if we discover an error when scrubbing in ro mode we a)
blindly increment the uncorrectable_errors counter, and b) spam the
dmesg with the 'unable to fixup (regular) error at ...' message, even
though a) we haven't tried to determine if the error is correctable or
not, and b) we haven't tried to fixup anything.  Fix this.

Cc: Stefan Behrens <sbehrens@giantdisaster.de>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>

fs/btrfs/scrub.c

@@ -938,8 +938,10 @@ static int scrub_handle_errored_block(struct scrub_block *sblock_to_check)
 				BTRFS_DEV_STAT_CORRUPTION_ERRS);
 	}
 
-	if (sctx->readonly && !sctx->is_dev_replace)
-		goto did_not_correct_error;
+	if (sctx->readonly) {
+		ASSERT(!sctx->is_dev_replace);
+		goto out;
+	}
 
 	if (!is_metadata && !have_csum) {
 		struct scrub_fixup_nodatasum *fixup_nodatasum;