clk: stm32mp1: add support of I2C6_K

Add support of missing I2C6_K with bit 3 of RCC_MC_APB5ENSETR =
I2C6EN: I2C6 peripheral clocks enable.

This patch allows customer to use I2C6 in SPL or in U-Boot
as other I2C instance, already support in clk driver.

Signed-off-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
Reviewed-by: Patrice Chotard <patrice.chotard@foss.st.com>
diff --git a/drivers/clk/clk_stm32mp1.c b/drivers/clk/clk_stm32mp1.c
index d4f1048..8a5bdcb 100644
--- a/drivers/clk/clk_stm32mp1.c
+++ b/drivers/clk/clk_stm32mp1.c
@@ -549,6 +549,7 @@
 	STM32MP1_CLK_SET_CLR(RCC_MP_APB4ENSETR, 16, USBPHY_K, _USBPHY_SEL),
 
 	STM32MP1_CLK_SET_CLR(RCC_MP_APB5ENSETR, 2, I2C4_K, _I2C46_SEL),
+	STM32MP1_CLK_SET_CLR(RCC_MP_APB5ENSETR, 3, I2C6_K, _I2C46_SEL),
 	STM32MP1_CLK_SET_CLR(RCC_MP_APB5ENSETR, 8, RTCAPB, _PCLK5),
 	STM32MP1_CLK_SET_CLR(RCC_MP_APB5ENSETR, 20, STGEN_K, _STGEN_SEL),