Fix retrieve user value in IOCTL_VALSET_NUM

Replace _IOW with _IO macro to reflect that IOCTL_VALSET_NUM passes
the integer value directly via arg, consistent with the calling
convention used throughout this codebase. Restore the handler to
assign arg directly to ioctl_num.

Author: applepwc

examples/ioctl.c

@@ -20,7 +20,7 @@ struct ioctl_arg {
 #define IOCTL_VALSET _IOW(IOC_MAGIC, 0, struct ioctl_arg)
 #define IOCTL_VALGET _IOR(IOC_MAGIC, 1, struct ioctl_arg)
 #define IOCTL_VALGET_NUM _IOR(IOC_MAGIC, 2, int)
-#define IOCTL_VALSET_NUM _IOW(IOC_MAGIC, 3, int)
+#define IOCTL_VALSET_NUM _IO(IOC_MAGIC, 3)
 
 #define IOCTL_VAL_MAXNR 3
 #define DRIVER_NAME "ioctltest"