Update loop.c to use a kthread instead of a deprecated kernel_thread for
loop devices.

[akpm@osdl.org: don't change the thread's name]
Signed-off-by: NSerge E. Hallyn <serue@us.ibm.com>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>