HID: hidraw: warn if userspace headers are outdated

Put a warning into sample hidraw code in samples/hidraw/hid-example.c
in case the userspace headers are missing the necessary defines and
need to be updated.

Signed-off-by: Jiri Kosina <[e-mail]>

samples/hidraw/hid-example.c

···
 /*
  * Ugly hack to work around failing compilation on systems that don't
  * yet populate new version of hidraw.h to userspace.
- *
- * If you need this, please have your distro update the kernel headers.
  */
 #ifndef HIDIOCSFEATURE
+#warning Please have your distro update the userspace kernel headers
 #define HIDIOCSFEATURE(len)    _IOC(_IOC_WRITE|_IOC_READ, 'H', 0x06, len)
 #define HIDIOCGFEATURE(len)    _IOC(_IOC_WRITE|_IOC_READ, 'H', 0x07, len)
 #endif