drm/msm/gpu: Set number of clocks to 0 if the list allocation fails

If we fail to allocate gpu->grp_clks reset the number of available
clocks to zero to avoid referencing the missing array later.

Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>