Btrfs, scrub: uninitialized variable in scrub_extent_for_parity()

The only way that "ret" is set is when we call scrub_pages_for_parity() so the skip to "if (ret) " test doesn't make sense and causes a static checker warning.

---
Static checker work. Not tested. There are some other valid looking warnings from the same file:

fs/btrfs/scrub.c:2933 scrub_raid56_parity() warn: XXX passing uninitialized 'extent_physical' fs/btrfs/scrub.c:2933 scrub_raid56_parity() warn: XXX passing uninitialized 'extent_dev' fs/btrfs/scrub.c:2933 scrub_raid56_parity() warn: XXX passing uninitialized 'extent_mirror_num'

index f2bb13a..9e1569f 100644
@@ -2607,9 +2607,9 @@ static int scrub_extent_for_parity(struct scrub_parity *sparity,
 		ret = scrub_pages_for_parity(sparity, logical, l, physical, dev,
 					     flags, gen, mirror_num,
 					     have_csum ? csum : NULL);
-skip:
 		if (ret)
 			return ret;
+skip:
 		len -= l;
 		logical += l;
 		physical += l;