hotplug: fix busy loop device detection

hotplug: fix busy loop device detection

Improve busy loop device detection after changeset 22773:02c0af2bf280

The intention is not to find the file to be mounted in the losetup -a
output.  What matters are existing mounted files with the same dev:inode
as the new file.  So the fix is to apply variable expansion which
happens only without double quotes.  Otherwise $dev will contain
newlines for hardlinked files, as mentioned in the commit message from
the changeset above.

losetup -a does also truncate long filenames to 62 chars due to ioctl
limitations.  This part is fixed with 2.6.37 where the filename can be
obtained from sysfs. As a result very long filenames will be missed.

Signed-off-by: Olaf Hering <olaf@aepfle.de>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>
Committed-by: Ian Jackson <ian.jackson@eu.citrix.com>