target: Use kmalloc_array() in compare_and_write_callback()

* A multiplication for the size determination of a memory allocation
  indicated that an array data structure should be processed.
  Thus use the corresponding function "kmalloc_array".

  This issue was detected by using the Coccinelle software.

* 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>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/target/target_core_sbc.c

@@ -519,8 +519,8 @@ static sense_reason_t compare_and_write_callback(struct se_cmd *cmd, bool succes
 		goto out;
 	}
 
-	write_sg = kmalloc(sizeof(struct scatterlist) * cmd->t_data_nents,
-			   GFP_KERNEL);
+	write_sg = kmalloc_array(cmd->t_data_nents, sizeof(*write_sg),
+				 GFP_KERNEL);
 	if (!write_sg) {
 		pr_err("Unable to allocate compare_and_write sg\n");
 		ret = TCM_OUT_OF_RESOURCES;