allwinner: Always use a 3MHz RSB bus clock

None of the other drivers (Linux, U-Boot, Crust) need to lower the bus
clock frequency to switch the PMIC to RSB mode. That logic is not needed
here, either. The hardware takes care of running this transaction at the
correct bus frequency.
Signed-off-by: Samuel Holland <samuel@sholland.org>
Change-Id: Idcfe933df4da75d5fd5a4f3e362da40ac26bdad1

plat/allwinner/sun50i_a64/sunxi_power.c

@@ -92,8 +92,8 @@ static int rsb_init(void)
 	if (ret)
 		return ret;
 
-	/* Start with 400 KHz to issue the I2C->RSB switch command. */
-	ret = rsb_set_bus_speed(SUNXI_OSC24M_CLK_IN_HZ, 400000);
+	/* Switch to the recommended 3 MHz bus clock. */
+	ret = rsb_set_bus_speed(SUNXI_OSC24M_CLK_IN_HZ, 3000000);
 	if (ret)
 		return ret;
 
@@ -105,11 +105,6 @@ static int rsb_init(void)
 	if (ret)
 		return ret;
 
-	/* Now in RSB mode, switch to the recommended 3 MHz. */
-	ret = rsb_set_bus_speed(SUNXI_OSC24M_CLK_IN_HZ, 3000000);
-	if (ret)
-		return ret;
-
 	/* Associate the 8-bit runtime address with the 12-bit bus address. */
 	ret = rsb_assign_runtime_address(AXP803_HW_ADDR,
 					 AXP803_RT_ADDR);