drm/r128/ati_pcigart: Source file headers are not good candidates for kernel-doc

Fixes the following W=1 kernel build warning(s):

drivers/gpu/drm/r128/ati_pcigart.c:2: warning: Cannot understand * file ati_pcigart.c

Cc: David Airlie <[e-mail]>
Cc: Daniel Vetter <[e-mail]>
Cc: Gareth Hughes <[e-mail]>
Cc: [e-mail]
Signed-off-by: Lee Jones <[e-mail]>
Signed-off-by: Sam Ravnborg <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/r128/ati_pcigart.c

···
-/**
+/*
  * \file ati_pcigart.c
  * ATI PCI GART support
  *