commit 1932b7be upstream.

A block-local variable stores error code but btrfs_get_blocks_direct may
not return it in the end as there's a ret defined in the function scope.

Fixes: d187663e ("Btrfs: lock extents as we map them in DIO")
Signed-off-by: David Sterba <dsterba@suse.cz>
Signed-off-by: Chris Mason <clm@fb.com>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>