log_sub_block_var: move fn ptr constant out of loop

This avoids reloading the value in the inner loop.

Change-Id: I84643da75e15576bb2727704884d9e447f14f679

av1/encoder/partition_search.c

diff --git a/av1/encoder/partition_search.c b/av1/encoder/partition_search.c
index 12eb5b8..b6f51d7 100644
--- a/av1/encoder/partition_search.c
+++ b/av1/encoder/partition_search.c
@@ -5413,13 +5413,13 @@
   double min_var_4x4 = (double)INT_MAX;
   double max_var_4x4 = 0.0;
 
+  aom_variance_fn_t vf = cpi->ppi->fn_ptr[BLOCK_4X4].vf;
   for (int i = 0; i < bh; i += MI_SIZE) {
     for (int j = 0; j < bw; j += MI_SIZE) {
       int var;
       // Calculate the 4x4 sub-block variance.
       var = av1_calc_normalized_variance(
-          cpi->ppi->fn_ptr[BLOCK_4X4].vf,
-          x->plane[0].src.buf + (i * x->plane[0].src.stride) + j,
+          vf, x->plane[0].src.buf + (i * x->plane[0].src.stride) + j,
           x->plane[0].src.stride, is_hbd);
 
       // Record min and max for over-arching block