Fix error: ‘access’ may be used uninitialized in this function
 [-Werror=maybe-uninitialized]
in GrGLGpu::bindImageStorage.

Found because this broke the compiles for the debugger, imageinfo, and fiddle, 
but apparently not any bots?

BUG=skia:

Change-Id: Id8f964bca4f6493428b35c1b64df468b9d1419db
Reviewed-on: https://skia-review.googlesource.com/5380
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Joe Gregorio <jcgregorio@google.com>
diff --git a/src/gpu/gl/GrGLGpu.cpp b/src/gpu/gl/GrGLGpu.cpp
index d3f13d0..4820ca8 100644
--- a/src/gpu/gl/GrGLGpu.cpp
+++ b/src/gpu/gl/GrGLGpu.cpp
@@ -3356,7 +3356,7 @@
     SkASSERT(texture);
     if (texture->uniqueID() != fHWBoundImageStorages[unitIdx].fTextureUniqueID ||
         ioType != fHWBoundImageStorages[unitIdx].fIOType) {
-        GrGLenum access;
+        GrGLenum access = GR_GL_READ_ONLY;
         switch (ioType) {
             case kRead_GrIOType:
                 access = GR_GL_READ_ONLY;