anv: Add DRM_RDWR flag in anv_gem_handle_to_fd
The DRM_RDWR flag is needed for mmap with PROT_WRITE to work. A similar change was done for libdrm in drm@05727548.
The DRM_RDWR flag is needed for mmap with PROT_WRITE to work. A similar change was done for libdrm in drm@05727548.