graw: fix logic error in pixel format selection

graw: fix logic error in pixel format selection

The loop to choose a pixel format for the window was incrementing
'i' after we succeeded in creating the window so if we chose format[0]
for graw_create_window_and_screen() we were putting format[1] in
the pipe_resource template for creating the render target.

This only worked because of the order of the elements in the formats[]
array.

The graw_xlib.c code now properly compares the requested gallium pixel
format against the visual's color layout.

Update all the graw demos to fix the off-by-one-i error.