btrfs: send: simplify return logic from is_inode_existent()

There is no need to have an 'out' label and jump into it since there are
no resource cleanups to perform (release locks, free memory, etc), so
make this simpler by removing the label and goto and instead return
directly.

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>