clk: imx: Add correct failure handling for clk based helpers

If the clk_hw based API returns an error, trying to return the clk from
hw will end up in a NULL pointer dereference. So adding the to_clk
checker and using it inside every clk based macro helper we handle that
case correctly.

This to_clk is also temporary and will go away along with the clk based
macro helpers once there is no user that need them anymore.

Signed-off-by: Abel Vesa <abel.vesa@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>