USB: serial: garmin_gps: Use flexible-array member

Old code in the kernel uses 1-byte and 0-byte arrays to indicate the presence of a "variable length array":

struct something {
    int length;
    u8 data[1];
};

struct something *instance;

instance = kmalloc(sizeof(*instance) + size, GFP_KERNEL); instance->length = size;
memcpy(instance->data, source, size);

There is also 0-byte arrays. Both cases pose confusion for things like sizeof(), CONFIG_FORTIFY_SOURCE, etc.[1] Instead, the preferred mechanism to declare variable-length types such as the one above is a flexible array member[2] which need to be the last member of a structure and empty-sized:

struct something {
        int stuff;
        u8 data[];
};

Also, by making use of the mechanism above, we will get a compiler warning in case the flexible array does not occur last in the structure, which will help us prevent some kind of undefined behavior bugs from being unadvertenly introduced[3] to the codebase from now on.

[1] https://github.com/KSPP/linux/issues/21
[2] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")

---
 drivers/usb/serial/garmin_gps.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index 633550ec3025..ffd984142171 100644
@@ -104,7 +104,7 @@ struct garmin_packet {
 	int               seq;
 	/* the real size of the data array, always > 0 */
 	int               size;
-	__u8              data[1];
+	__u8              data[];
 };
 
 /* structure used to keep the current state of the driver */

2.23.0

Applied, thanks.

Johan