i2c: imx: Remove clk_get_rate for each transfer again

As clk_get_rate() also keeps the clk prepare lock which can lead into a
deadlock. It was removed upstream with this commit:
(90ad2cbe) i2c: imx: use clk notifier for rate changes

But it has been readded again with:
(d2561688) MLK-20368 i2c-imx: Coverity: fix divide by zero warning

The commit message does not explain why it was readded. It is not needed
as the clk notifier is used. Removed it again.

REFERENCE: https://github.com/nxp-imx/linux-imx/pull/21