btrfs: merge btrfs_find_device and find_device

commit 09ba3bc9dd150457c506e4661380a6183af651c1 upstream.

Both btrfs_find_device() and find_device() does the same thing except
that the latter does not take the seed device onto account in the device
scanning context. We can merge them.

Signed-off-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
[4.19.y backport notes:
Vikash : - To apply this patch, a portion of commit e4319cd9cace
           was used to change the first argument of function
           "btrfs_find_device" from "struct btrfs_fs_info" to
           "struct btrfs_fs_devices".
Signed-off-by: Vikash Bansal <bvikas@vmware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>