drm: Remove unused branch in legacy PCI initialization

The legacy PCI init code sets the drvdata for drivers with MODESET
flag, but none of the old UMS drivers sets the flag. Remove the branch.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210516191918.20974-1-tzimmermann@suse.de