msm: vidc: do not update operating rate during INT_MAX

INT_MAX is an interface provided to client to configure
video session in TURBO mode. When client configures the
operating rate as INT_MAX, the rate at which the frames
arrive at video driver does not change, so there is no
need to update the operating rate.
If the operating rate is updated, macroblocks/s for the
session goes high. As a result, the session gets rejected
as the clock is not sufficient for high mbs/s.

Change-Id: Iaa48073a486ce6435664a6afb8a4c6ddd7b7f87d
Signed-off-by: Vikash Garodia <vgarodia@codeaurora.org>