clk: qcom: mdss: fix regmap range for dsi pll driver

Currently in dsi pll driver the maximum range of regmap pll
config is wrong. This causes issues when someone tries to
read the full register dump from regmap sysfs node. Fix
this by putting proper register range in driver.

Change-Id: I6091c96187634f1d82c3ae1f463cc80604954113
Signed-off-by: Sandeep Panda <spanda@codeaurora.org>