mx7: clock: Use 60MHz for the I2C clocks

mx7: clock: Use 60MHz for the I2C clocks

When an I2C clock is enabled inside enable_i2c_clk() the clock rate is
configured as PLL_SYS_MAIN_120M_CLK / 2 = 60MHz.

Currently, the I2C clock is retrieved from I2C1_CLK_ROOT, which
may not be the one that was enabled.

As there is no clock driver for the imx7d, it is better to return 60MHz
for the I2C clock.

This provides a workaround for the imx7d-pico board, where I2C4 is
connected to the PMIC.

With this change, it is possible to convert the imx7d-pico board
to DM_I2C and DM_PMIC.

Signed-off-by: Fabio Estevam <festevam@denx.de>