Add return to SkBoxBlurGetPlatformProcs_SSE4.

This fixes Android build.

R=reed@google.com, mtklein@google.com

Author: scroggo@google.com

Review URL: https://codereview.chromium.org/378613002
diff --git a/src/opts/SkBlurImage_opts_SSE4.cpp b/src/opts/SkBlurImage_opts_SSE4.cpp
index fb17aac..1b99038 100644
--- a/src/opts/SkBlurImage_opts_SSE4.cpp
+++ b/src/opts/SkBlurImage_opts_SSE4.cpp
@@ -117,6 +117,7 @@
                                     SkBoxBlurProc* boxBlurXY,
                                     SkBoxBlurProc* boxBlurYX) {
     sk_throw();
+    return false;
 }