There was a switch/case left that hadn't
yet been replaced by Context::getBuffer,
so I fixed that.

Change-Id: I71bca410322e1cfc130a2753d738c3b64fb271c5
Reviewed-on: https://swiftshader-review.googlesource.com/3544Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>