clk: stm32: Add clk entry for SDMMC2 on stm32F769

STM32F769 has 2 SDMMC port, add clock entry for the second one.

Signed-off-by: Alexandre TORGUE <alexandre.torgue@st.com>
Signed-off-by: Patrice Chotard <patrice.chotard@st.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>