auxdisplay: linedisp: Use kmemdup_nul() helper

Use the existing kmemdup_nul() helper instead of open-coding the same
operation.

Signed-off-by: Geert Uytterhoeven <[e-mail]>
Signed-off-by: Miguel Ojeda <[e-mail]>

drivers/auxdisplay/line-display.c

···
 		return 0;
 	}
 
-	new_msg = kmalloc(count + 1, GFP_KERNEL);
+	new_msg = kmemdup_nul(msg, count, GFP_KERNEL);
 	if (!new_msg)
 		return -ENOMEM;
-
-	memcpy(new_msg, msg, count);
-	new_msg[count] = 0;
 
 	kfree(linedisp->message);