Staging: hv: rework use of workqueues in osd

Change the usage of workqueues to be consistant with other parts of
the kernel.

Signed-off-by: Bill Pemberton <wfp5p@virginia.edu>
Cc: Hank Janssen <hjanssen@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>