gralloc: Default to an error value for mapFrameBuffer

We do further operations in fb_device_open based on the result of
mapFrameBuffer. However, if mapFrameBuffer is never done, we
could end up with a random crash when using the info values in
fb_device_open. Defaulting to an error value avoids this.

Change-Id: I1e51f814611a3f2eb73f36d75e14d8725ca98474
1 file changed