Eliminate a warning

arch @ 2b89cb7d

-Subproject commit 0761b677efa861b6369cea195968a59e4a6e6860
+Subproject commit 2b89cb7d768c94c11a3902e85fd0858c4033ef74

configs @ dd63cfca

-Subproject commit 16d7a0dab2c4a48583d40bcf1dbf8e9a74316e91
+Subproject commit dd63cfca08a5a3baf8e829080bf9580723765566

drivers/serial/serial.c

@@ -900,7 +900,7 @@ static int uart_ioctl(FAR struct file *filep, int cmd, unsigned long arg)
 
               irqrestore(state);
 
-              *(int *)arg = count;
+              *(FAR int *)((uintptr_t)arg) = count;
               ret = 0;
             }
             break;
@@ -923,7 +923,7 @@ static int uart_ioctl(FAR struct file *filep, int cmd, unsigned long arg)
 
               irqrestore(state);
 
-              *(int *)arg = count;
+              *(FAR int *)((uintptr_t)arg) = count;
               ret = 0;
             }
             break;