adreno_tz: Fix divide by zero problem in gpu_load_show()

If the acc_total value is zero then kernel would crash on
div-by-zero. Add better input validation in gpu_load_show()
to avoid divide by zero problem.

CRs-Fixed: 1092584
Change-Id: I7affbd797bf4b0025f718c757043b36f392dae5b
Signed-off-by: Sudeep Yedalapure <sudeepy@codeaurora.org>