Fix incorrect use of uv eobs in intra modes

In vp8_rd_pick_inter_mode(), if total of eobs is zero, rate needs
to be adjusted since there are no non-zero coefficients for
transmission. The uv intra eobs calculated in
rd_pick_intra_mbuv_mode() need to be saved before they are
overwritten by inter-mode eobs.

Change-Id: I41dd04fba912e8122ef95793d4d98a251bc60e58