modesetting: workaround for stride/pitch mismatch
This helps for the cases where buffer stride is miscalculated, the most notable example being 1366x768 resolution. From what I understand the code, the stride calculation should distinguish between any pixmap and the one used for FB, which is not the case and everything is calculated in glamor/glamor.c:227.
Fixes: #889 (closed) Signed-off-by: Aleksander Miera ammiera@hotmail.com