btrfs: remove pointless WARN_ON() in cache_save_setup()

btrfs: remove pointless WARN_ON() in cache_save_setup()

This WARN_ON(ret) is never executed since the previous if statement makes
us jump into the 'out_put' label when ret is not zero. The existing
transaction abort inside the if statement also gives us a stack trace,
so we don't need to move the WARN_ON(ret) into the if statement either.

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