frameworks/rs: fix typos and clang-tidy warnings

This change fixes a few typos and clang tidy warnings related to the
"llvm-namespace-comment" checks.

Bug: 26936282
Test: WITH_TIDY=1 WITH_TIDY_CHECKS="llvm-namespace-comment" mm
Change-Id: Ic65182e5b4999fbd48d6a8ad7172e4bfeeb541f4
diff --git a/rsMutex.h b/rsMutex.h
index 47725d7..3b5d616 100644
--- a/rsMutex.h
+++ b/rsMutex.h
@@ -36,8 +36,8 @@
     pthread_mutex_t mMutex;
 };
 
-}
-}
+} // namespace renderscript
+} // namespace android
 
 #endif