msm: display: reduce pwm frquency to fix the broswer blank issue

screen goes completely blank while loading a webpage at low back
light value. reducing the pwm frequency range to fix the issue.

Signed-off-by: Siddhartha Agrawal <agrawals@codeaurora.org>
Change-Id: I44018b9f19d2dd3c8731d94588c606cd081fa3cb
CRs-fixed: 362987