msm: tsc: Allow driver to work without bus scaling

The TSC driver uses the bus scaling API to request bus
bandwidth. However, the bus scaling feature may be completely disabled.
In this case, allow the TSC driver to operate as usual.

Change-Id: I0781213dd9131efd94a30670fa4ddb0a6c70d7db
Signed-off-by: Liron Kuch <lkuch@codeaurora.org>