v4l2: Define ioctl_req_t for posix/linux case

this is an issue seen with musl based linux distros e.g. alpine [1]
musl is not going to change this since it breaks ABI/API interfaces
Newer compilers are stringent ( e.g. clang16 ) which can now detect
signature mismatches in function pointers too, existing code warned but
did not error with older clang

Fixes
gstv4l2object.c:544:23: error: incompatible function pointer types assigning to 'gint (*)(gint, ioctl_req_t, ...)' (aka 'int (*)(int, unsigned long, ...)') from 'int (int, int, ...)' [-Wincompatible-function-pointer-types]
    v4l2object->ioctl = ioctl;
                      ^ ~~~~~

[1] https://gitlab.alpinelinux.org/alpine/aports/-/issues/7580

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/3950>

subprojects/gst-plugins-good/sys/v4l2/gstv4l2object.h

@@ -76,6 +76,8 @@ typedef gboolean  (*GstV4l2UpdateFpsFunction) (GstV4l2Object * v4l2object);
  * 'unsigned long' for the 2nd parameter */
 #ifdef __ANDROID__
 typedef unsigned ioctl_req_t;
+#elif defined(__linux__) && !defined(__GLIBC__) /* musl/linux */
+typedef int ioctl_req_t;
 #else
 typedef gulong ioctl_req_t;
 #endif