[SCSI] scsi_debug: Fix 32-bit overflow in do_device_access causing memory corruption

If I create a scsi_debug device that is larger than 4GB, the multiplication of
(block * scsi_debug_sector_size) can produce a 64-bit value.  Unfortunately,
the compiler sees two 32-bit quantities and performs a 32-bit multiplication,
thus truncating the bits above 2^32.  This causes the wrong memory location to
be read or written.  Change block and rest to be unsigned long long.

Signed-off-by: Darrick J. Wong <djwong@us.ibm.com>
Acked-by: Douglas Gilbert <dgilbert@interlog.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>