fsl/fman: Fix clk reference leak in read_dts_node()

In the Linux kernel, the following vulnerability has been resolved: fsl/fman: Fix clk reference leak in read_dts_node() of_clk_get() returns a clock with its reference count incremented, but read_dts_node() only uses it to read the rate and never calls clk_put(). The clock is not stored anywhere, so the reference cannot be released later either. Release the clock once its rate has been read, which also covers the error path taken when the rate is zero.