clk: qcom: lcc-msm8960: Fix PLL rate detection

regmap_read() returns 0 on success, not the value of the register
that is read. Fix it so we properly detect the frequency plan.

Fixes: b82875ee "clk: qcom: Add MSM8960/APQ8064 LPASS clock
controller (LCC) driver"
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Michael Turquette <mturquette@linaro.org>