msm: kgsl: Return error when getting pdata of bus scale table fails

Failure to get pdata for bus is an error condition, ensure that
this failure is indicated to the calling function by returning
invalid error instead of returning success when the failure is
indicated by NULL value in the bus scale table pointer

Change-Id: I1624dd94969eb8f713d64bda169d837451c2f040
Signed-off-by: Shubhraprakash Das <sadas@codeaurora.org>