udev: define BTN_DPAD_RIGHT if not present (#6267)

Regression introduced in commit b876bc0 when building on systemds with a pre
3.11 headers (RHEL7 and derivatives).

All the DPAD defines were introduced in the same kernel commit
d09bbfd2a8408a9954, we don't need a separate ifdef check for right.

Fixes #6240

src/udev/udev-builtin-input_id.c

@@ -47,6 +47,7 @@
 /* available as of kernel 3.11 */
 #ifndef BTN_DPAD_UP
 #define BTN_DPAD_UP 0x220
+#define BTN_DPAD_RIGHT 0x223
 #endif /* BTN_DPAD_UP */
 
 /* available as of kernel 3.13 */