mmc: mmc_test: Use kcalloc() in mmc_test_alloc_mem()

* The script "checkpatch.pl" pointed information out like the following.

  WARNING: Prefer kcalloc over kzalloc with multiply

  Thus fix the affected source code place.

* Replace the specification of a data structure by a pointer dereference
  to make the corresponding size determination a bit safer according to
  the Linux coding style convention.

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Shawn Lin <shawn.lin@rock-chips.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/core/mmc_test.c

@@ -360,8 +360,7 @@ static struct mmc_test_mem *mmc_test_alloc_mem(unsigned long min_sz,
 	if (!mem)
 		return NULL;
 
-	mem->arr = kzalloc(sizeof(struct mmc_test_pages) * max_segs,
-			   GFP_KERNEL);
+	mem->arr = kcalloc(max_segs, sizeof(*mem->arr), GFP_KERNEL);
 	if (!mem->arr)
 		goto out_free;