drivers: msm_lmh_dcvs: Fix unsigned integer overflow error

The frequency value that is calculated in Hz can be of a large value to
cause unsigned integer overflow. DCVSh though fetches the final
frequency value in HZ in a unsigned long variable, the intermediate
variable used in the estimation is unsigned integer. This will result in
a wrong frequency value being reported to userspace and clients.

Fix the overflow by using a unsigned long datatype for the frequency
computation.

Change-Id: I4bba53b9f5bd243c4aaaf67a831ce77ef231b38f
Signed-off-by: Ram Chandrasekar <rkumbako@codeaurora.org>