Only sync the filesystem containing the initramfs
This avoids update-initramfs taking an unnecessarily long time if there is lots of activity on a different filesystem, or even hanging in cases such as a stale NFS mount.
Based on a patch by Jukka Tastula poltsy@gmail.com.
Closes: #882380 LP: #1667512 Signed-off-by: Colin Watson cjwatson@debian.org