simplify making translate only invmatrix

BUG=
R=humper@google.com

Review URL: https://codereview.chromium.org/23875010

git-svn-id: http://skia.googlecode.com/svn/trunk@11114 2bbb7eff-a529-9590-31e7-b0007b416f81

src/core/SkBitmapProcState.cpp

@@ -179,8 +179,8 @@ void SkBitmapProcState::possiblyScaleImage() {
 
         // set the inv matrix type to translate-only;
 
-        fInvMatrix.setTranslate( 1/fInvMatrix.getScaleX() * fInvMatrix.getTranslateX(),
-                                 1/fInvMatrix.getScaleY() * fInvMatrix.getTranslateY() );
+        fInvMatrix.setTranslate(fInvMatrix.getTranslateX() / fInvMatrix.getScaleX(),
+                                fInvMatrix.getTranslateY() / fInvMatrix.getScaleY());
 
         // no need for any further filtering; we just did it!