scsi: scsi_debug: Weaken rwlock around ramdisk access

The design of this driver is to do any ramdisk access on the same thread
that invoked the queuecommand() call. That is assumed to be user space
context. The command duration is implemented by setting the delay with a
high resolution timer. The hr timer's callback may well be in interrupt
context, but it doesn't touch the ramdisk. So try removing the
_irqsave()/_irqrestore() portion on the read-write lock that protects
ramdisk access.

Link: https://lore.kernel.org/r/20200421151424.32668-5-dgilbert@interlog.com


Signed-off-by: Douglas Gilbert <dgilbert@interlog.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>