Update STM32 RNGEN register bit name to more closely match documentation.

examples/stm32/f4/stm32f4-discovery/random/random.c

@@ -40,7 +40,7 @@ static void rng_setup(void)
 	/* Enable the random number generation by setting the RNGEN bit in the RNG_CR
 	register. This activates the analog part, the RNG_LFSR and the error detector.
 	*/
-	RNG_CR |= RNG_CR_EN;
+	RNG_CR |= RNG_CR_RNGEN;
 }
 
 static void gpio_setup(void)

include/libopencm3/stm32/f4/rng.h

@@ -36,7 +36,7 @@
 /* --- RNG_CR values ------------------------------------------------------- */
 
 /* RNG ENABLE */
-#define RNG_CR_EN			(1 << 2)
+#define RNG_CR_RNGEN		(1 << 2)
 
 /* RNG interupt enable */
 #define RNG_CR_IE			(1 << 3)