Fixed overflow test on boost calculation

Normalization of the frame boost value was being done
when it reached the value 1028. The intention was to
keep to a range of 10 bits, so it should have been
clipped above 1023.

Change-Id: I0afdddc1d2eb9e7822ec4578903cbe6ec0b33b91

vp9/encoder/vp9_firstpass.c

@@ -1963,7 +1963,7 @@ static void define_gf_group(VP9_COMP *cpi, FIRSTPASS_STATS *this_frame) {
         (cpi->baseline_gf_interval * 100) + (boost - 100);
 
     // Prevent overflow
-    if (boost > 1028) {  // TODO(agrange) Should this be 1024?
+    if (boost > 1023) {
       int divisor = boost >> 10;
       boost /= divisor;
       allocation_chunks /= divisor;