rng: stm32: update STM32MP15 max RNG clock frequency

RNG max clock frequency can be updated to 48MHz according to latest
tests.

Change-Id: Ieb2faa06d07631cca69fc487673a61aad964c6d7
Signed-off-by: Gatien Chevallier <gatien.chevallier@foss.st.com>
Reviewed-on: https://gerrit.st.com/c/mpu/oe/st/u-boot/+/363093
ACI: CIBUILD <MDG-smet-aci-builds@list.st.com>
Reviewed-by: Patrice CHOTARD <patrice.chotard@foss.st.com>
ACI: CITOOLS <MDG-smet-aci-reviews@list.st.com>
Domain-Review: Gatien CHEVALLIER <gatien.chevallier@st.com>
Tested-by: Amit MITTAL <amit.mittal@st.com>
Reviewed-by: Gatien CHEVALLIER <gatien.chevallier@st.com>

Author: GseoC

drivers/rng/stm32mp1_rng.c

@@ -210,7 +210,7 @@ static const struct stm32_rng_data stm32mp13_rng_data = {
 
 static const struct stm32_rng_data stm32_rng_data = {
 	.has_cond_reset = false,
-	.max_clock_rate = 3000000,
+	.max_clock_rate = 48000000,
 };
 
 static const struct udevice_id stm32_rng_match[] = {