drm/pl111/pl111_debugfs: Make local function 'pl111_debugfs_regs()' static

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

 drivers/gpu/drm/pl111/pl111_debugfs.c:33:5: warning: no previous prototype for ‘pl111_debugfs_regs’ [-Wmissing-prototypes]

Cc: Eric Anholt <eric@anholt.net>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20201116174112.1833368-24-lee.jones@linaro.org

drivers/gpu/drm/pl111/pl111_debugfs.c

@@ -30,7 +30,7 @@ static const struct {
 	REGDEF(CLCD_PL111_LCUR),
 };
 
-int pl111_debugfs_regs(struct seq_file *m, void *unused)
+static int pl111_debugfs_regs(struct seq_file *m, void *unused)
 {
 	struct drm_info_node *node = (struct drm_info_node *)m->private;
 	struct drm_device *dev = node->minor->dev;