[SCSI] sd: Do not call do_div() with a 64-bit divisor

do_div() is meant for divisions of 64-bit number by 32-bit numbers.
Passing 64-bit divisor types caused issues in the past on 32-bit platforms,
cfr. commit ea077b1b ("m68k: Truncate base
in do_div()").

As scsi_device.sector_size is unsigned (int), factor should be unsigned
int, too.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>