[SCSI] scsi_debug: virtual_gb ignores sector_size

In the scsi_debug driver, the virtual_gb option ignores the
sector_size, implicitly assuming that is 512 bytes.  So if
'virtual_gb=1 sector_size=4096' the result is an 8 GB (virtual) disk.

Signed-off-by: Douglas Gilbert <dgilbert@interlog.com>
Cc: Stable Tree <stable@kernel.org>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>