Don't use extra lines for r=2 guided filter

Changes the CONFIG_FAST_SGR=1 strategy to not use any
subsampling for the r=1 filter, but for the r=2 filter
sub-sample vertically but combine only by filtering
horizontally in the last stage for odd rows.

Coding efficiency loss sems quite minimal.

Change-Id: I5644ac400b387c37a2d278db7f6ad3ac0a6b5e93

av1/encoder/pickrst.c

@@ -353,7 +353,7 @@ static void sgr_filter_block(const sgr_params_type *params, const uint8_t *dat8,
                              int width, int height, int dat_stride,
                              int use_highbd, int bit_depth, int32_t *flt1,
                              int32_t *flt2, int flt_stride) {
-#if CONFIG_FAST_SGR == 2
+#if CONFIG_FAST_SGR
   av1_selfguided_restoration_c(dat8, width, height, dat_stride, flt1, flt2,
                                flt_stride, params, bit_depth, use_highbd);
 #else