drm: Fix build error caused by missing drm_nomodeset.o

The patch for commit 6a2d2dd ("drm: Move nomodeset kernel parameter
to the DRM subsystem") was generated with config 'diff.noprefix true'.

But later was applied using 'cat nomodeset.mbox | dim apply-branch' on a
machine with 'diff.noprefix false'. And command 'git am --scissors -3' as
used by the dim tool doesn't handle that case well, since the 3-way merge
wrongly resolves the path for new file drivers/gpu/drm/drm_nomodeset.c as
gpu/drm/drm_nomodeset.c instead.

It led to the following build error as reported by the kernel test robot:

  make[4]: *** No rule to make target 'drivers/gpu/drm/drm_nomodeset.o', needed by 'drivers/gpu/drm/built-in.a'.

Fixes: 6a2d2dd ("drm: Move nomodeset kernel parameter to the DRM subsystem")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20211127191910.709356-1-javierm@redhat.com