Add call to aom_clear_system_state()

Added aom_clear_system_state() in the function
setup_planes() before floating point instructions.

BUG=aomedia:2956

Change-Id: I21d07e64fcb766d1f3e9bacf0093dc2c849d305c
(cherry picked from commit ff5d8dd973dde866fa93bb200547ac69575832b4)

av1/encoder/var_based_part.c

diff --git a/av1/encoder/var_based_part.c b/av1/encoder/var_based_part.c
index 7fd94a2..025e125 100644
--- a/av1/encoder/var_based_part.c
+++ b/av1/encoder/var_based_part.c
@@ -812,6 +812,7 @@
 
   // Pick the ref frame for partitioning, use golden frame only if its
   // lower sad.
+  aom_clear_system_state();
   if (*y_sad_g < 0.9 * *y_sad) {
     av1_setup_pre_planes(xd, 0, yv12_g, mi_row, mi_col,
                          get_ref_scale_factors(cm, GOLDEN_FRAME), num_planes);