opencl fix: Restore support for subframes < 3
opencl fix: Restore support for subframes < 3

When number of sub frames configured is less than 3, the support for
gpu is broken. This is fixed.

Change-Id: I64865fdaa3de6bff41f895ca2a23057fff1559f3

ittiamvpx/libvpx-1,ittiamvpx/libvpx-1,ittiamvpx/libvpx-1,ittiamvpx/libvpx-1,ittiamvpx/libvpx-1,ittiamvpx/libvpx-1