FW recommended timeout for all mbox command is 30s.  Use msleep instead
mdelay to relinquish CPU when polling for mbox completion.
Signed-off-by: NJitendra Bhivare <jitendra.bhivare@avagotech.com>
Reviewed-by: NHannes Reinecke <hare@suse.com>
Signed-off-by: NMartin K. Petersen <martin.petersen@oracle.com>