scsi: target: use #define for xcopy descriptor len

Link: https://lore.kernel.org/r/20200327141954.955-2-ddiss@suse.de
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: David Disseldorp <ddiss@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/target/target_core_xcopy.c

@@ -134,7 +134,7 @@ static int target_xcopy_parse_tiddesc_e4(struct se_cmd *se_cmd, struct xcopy_op
 	 * Assigned designator
 	 */
 	desig_len = desc[7];
-	if (desig_len != 16) {
+	if (desig_len != XCOPY_NAA_IEEE_REGEX_LEN) {
 		pr_err("XCOPY 0xe4: invalid desig_len: %d\n", (int)desig_len);
 		return -EINVAL;
 	}