do_div is the wrong way to divide a sector_t, as it is less
efficient when sector_t is 32-bit wide. With the upcoming
do_div optimizations, the kernel starts warning about this:
drivers/scsi/scsi_debug.c: In function 'dif_store':
include/asm-generic/div64.h:207:28: warning: comparison of distinct pointer types lacks a cast
This changes the code to use sector_div instead, which always
produces optimal code.
Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>