drm: use correct dev node location in comment

Current comment mentions /dev/drm which hasn't been a thing even before
the code was merged into the kernel ;-)

v2: drop explicit node path (Sean)
Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Sean Paul <sean@poorly.run>
Link: https://patchwork.freedesktop.org/patch/msgid/20190722165648.7828-1-emil.l.velikov@gmail.com

drivers/gpu/drm/drm_file.c

@@ -285,7 +285,7 @@ static int drm_cpu_valid(void)
 }
 
 /*
- * Called whenever a process opens /dev/drm.
+ * Called whenever a process opens a drm node
  *
  * \param filp file pointer.
  * \param minor acquired minor-object.