drm/nouveau: drop use of DRM_UDELAY

The DRM_UDELAY is a simple wrapper for udealy() and to be consistent
call udelay() direct like in may other places.
This avoids the need to pull in drm_os_linux.h when we later
drop drmP.h uses in nouveau.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Cc: Ben Skeggs <bskeggs@redhat.com>
Cc: nouveau@lists.freedesktop.org
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/nouveau_dma.c

@@ -118,7 +118,7 @@ nv50_dma_push_wait(struct nouveau_channel *chan, int count)
 		}
 
 		if ((++cnt & 0xff) == 0) {
-			DRM_UDELAY(1);
+			udelay(1);
 			if (cnt > 100000)
 				return -EBUSY;
 		}