btrfs: remove redundant check on ret and goto

The check for a non-zero ret is redundant as the goto will jump to
the very next statement anyway.  Remove this extraneous code.

Detected by CoverityScan, CID#1463784 ("Identical code for different
branches")

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: David Sterba <dsterba@suse.com>