vpx_int_pro_row_c: add an assert for height
vpx_int_pro_row_c: add an assert for height

this quiets a static analysis warning with clang 11:

vpx_dsp/avg.c:353:15: warning: Assigned value is garbage or undefined
[core.uninitialized.Assign]
    hbuf[idx] /= norm_factor;
              ^  ~~~~~~~~~~~

the same fix was applied in libaom:
1ad0889bc aom_int_pro_row_c: add an assert for height

Bug: b/229626362
Change-Id: Ic8a249f866b33b02ec9f378581e51ac104d97169

webmproject/libvpx,webmproject/libvpx,webmproject/libvpx,webmproject/libvpx,webmproject/libvpx,webmproject/libvpx