Loading RGBA8 was apparently copying each
line "width" times, which is pretty bad.
Fixed that by removing the useless loop.

Change-Id: Icf38232e422eb33f77b9df499e4137ea8f53abd3
Reviewed-on: https://swiftshader-review.googlesource.com/3040Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>