Define backlight pin for Quefrency Rev2 (#8141)

keyboards/keebio/quefrency/rev2/config.h

@@ -46,6 +46,8 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 /* Set 0 if debouncing isn't needed */
 #define DEBOUNCE 5
 
+#define BACKLIGHT_PIN B5
+
 /* serial.c configuration for split keyboard */
 #define SOFT_SERIAL_PIN D0