clk/qcom: ipq4019: return valid rate when setting UART clock

clk/qcom: ipq4019: return valid rate when setting UART clock

clk_set_rate() should return the clock rate that was set. The IPQ4019
clock driver doesn't set any rates yet but it should still return the
expected value so that drivers can work properly.

For a baud rate of 115200 with an expected bit clock divisor of 16, the
clock rate should be 1843200 so return that frequency.

Signed-off-by: Caleb Connolly <caleb.connolly@linaro.org>