dt-bindings: mfd: stm32f4: Fix STM32F4_X_CLOCK() macro

Macro to select a clock was not correct.

Offset of enable register starts at 0x30, then calculation to select a bit is:
(@enable_reg - 0x30) / 4 * 32 + bit_to_select

Tested-by: M'boumba Cedric Madianga <cedric.madianga@gmail.com>
Acked-by: Stephen Boyd <sboyd@codeaurora.org>
Acked-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Gabriel Fernandez <gabriel.fernandez@st.com>
Signed-off-by: Alexandre TORGUE <alexandre.torgue@st.com>