btrfs-progs: completion: use _filedir to replace _btrfs_devs

For developers it's pretty common to call "btrfs check" on a raw image
dump other than real block device.  It's also possible to end users to
do some tests on loop devices.

So current _btrfs_devs() is really making things worse. Use _filedir()
to replace _btrfs_devs() so it can complete any filenames, no matter if
it's just a file or a real block device.

Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

btrfs-completion

@@ -4,13 +4,6 @@
 # (http://lists.alioth.debian.org/pipermail/bash-completion-devel/2013-June/004868.html)
 # edited by John C F <john.ch.fr at gmail.com> on 2015-02-02
 
-_btrfs_devs()
-{
-	local DEVS
-	DEVS=''; while read dev; do DEVS+="$dev "; done < <(lsblk -pnro name)
-	COMPREPLY+=( $( compgen -W "$DEVS" -- "$cur" ) )
-}
-
 _btrfs_mnts()
 {
 	local MNTS
@@ -68,14 +61,14 @@ _btrfs()
 				opts="$commands_scrub"
 				;;
 			check)
-				_btrfs_devs
+				_filedir
 				return 0
 				;;
 			rescue)
 				opts="$commands_rescue"
 				;;
 			restore)
-				_btrfs_devs
+				_filedir
 				return 0
 				;;
 			inspect-internal)
@@ -120,13 +113,13 @@ _btrfs()
 						;;
 					label)
 						_btrfs_mnts
-						_btrfs_devs
+						_filedir
 						return 0
 						;;
 				esac
 				;;
 			device|rescue)
-				_btrfs_devs
+				_filedir
 				return 0
 				;;
 			inspect-internal)
@@ -156,7 +149,7 @@ _btrfs()
 						return 0
 						;;
 					start)
-						_btrfs_devs
+						_filedir
 						return 0
 						;;
 				esac