gpu: host1x: Make host1x_cdma_wait_pushbuffer_space() static

The host1x_cdma_wait_pushbuffer_space() function is not declared or
directly called from outside the file it is in, so make it static.

Fixes the following sparse warning:

    drivers/gpu/host1x/cdma.c:235:5: warning: symbol 'host1x_cdma_wait_pushbuffer_space' was not declared. Should it be static?
Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
Signed-off-by: Thierry Reding <treding@nvidia.com>

drivers/gpu/host1x/cdma.c

@@ -232,7 +232,7 @@ unsigned int host1x_cdma_wait_locked(struct host1x_cdma *cdma,
  *
  * Must be called with the cdma lock held.
  */
-int host1x_cdma_wait_pushbuffer_space(struct host1x *host1x,
+static int host1x_cdma_wait_pushbuffer_space(struct host1x *host1x,
 					     struct host1x_cdma *cdma,
 					     unsigned int needed)
 {