Fix SubGopSwitchingTestLarge.

In an earlier MR, frame count for this test was reduced from 200 to 100,
in order to speed it up. However, some of these tests seem to need more
frames.

So, increased the frame count to 175.

Change-Id: I1eb65e6afed9e000975e51a1535de98aba89395d
diff --git a/test/subgop_test.cc b/test/subgop_test.cc
index 731784f..589cade 100644
--- a/test/subgop_test.cc
+++ b/test/subgop_test.cc
@@ -956,7 +956,7 @@
 
 TEST_P(SubGopSwitchingTestLarge, SubGopSwitching) {
   std::unique_ptr<libaom_test::VideoSource> video;
-  const unsigned int kFrames = 100;
+  const unsigned int kFrames = 175;
 
   if (is_extension_y4m(test_params_.input_file)) {
     video.reset(