drm: do not mask out DRM_FORMAT_BIG_ENDIAN

framebuffer_check() expects that drm_get_format_info() will not fail if
the __drm_format_info() call was successful.  That'll work only in case
both are called with the same pixel_format value, so masking out the
DRM_FORMAT_BIG_ENDIAN flag isn't a good idea.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20180905060445.15008-4-kraxel@redhat.com