drm/fb-helper: Fix the dummy remove_conflicting_framebuffers

We always need to remove conflicting framebuffers if any other fb driver
is enabled, and not just if we are setting up an fbdev ourselves.

Unfortunately remove_conflicting_framebuffers() was incorrectly stubbed
out if !fbdev rather than !fb leading to major memory corruption (and
corrupt filesystems) upon boot.

Fixes: 44adece5

 ("drm/fb-helper: Add a dummy remove_conflicting_framebuffers")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Tobias Jakobi <tjakobi@math.uni-bielefeld.de>
Cc: Noralf Trønnes <noralf@tronnes.org>
Cc: tomi.valkeinen@ti.com
Cc: dh.herrmann@gmail.com
Cc: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20160822204452.2509-1-chris@chris-wilson.co.uk