drm/vmwgfx: inline access to the pages from the piter

The indirection doesn't make sense because we always go through
the same function pointer. Instead of the extra indirection
lets inline the access to the current page.

Signed-off-by: Zack Rusin <zackr@vmware.com>
Reviewed-by: Martin Krastev <krastevm@vmware.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210609172307.131929-7-zackr@vmware.com