IB/iser: use sector_div instead of do_div

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/infiniband/ulp/iser/iser_verbs.c:1296:4: note: in expansion of macro 'do_div'
include/asm-generic/div64.h:224:22: warning: passing argument 1 of '__div64_32' from incompatible pointer type

This changes the code to use sector_div instead, which always
produces optimal code.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Sagi Grimberg <sagig@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>

drivers/infiniband/ulp/iser/iser_verbs.c

@@ -1293,7 +1293,7 @@ u8 iser_check_task_pi_status(struct iscsi_iser_task *iser_task,
 		if (mr_status.fail_status & IB_MR_CHECK_SIG_STATUS) {
 			sector_t sector_off = mr_status.sig_err.sig_err_offset;
 
-			do_div(sector_off, sector_size + 8);
+			sector_div(sector_off, sector_size + 8);
 			*sector = scsi_get_lba(iser_task->sc) + sector_off;
 
 			pr_err("PI error found type %d at sector %llx "