drm/tinydrm: make function st7586_pipe_enable static

The function st7586_pipe_enable  is local to the source
and does not need to be in global scope, so make it static.

Cleans up sparse warning:
symbol 'st7586_pipe_enable' was not declared. Should it be static?
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-By: David Lechner <david@lechnology.com>
[noralf: fixed: Alignment should match open parenthesis]
Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20170816092306.10969-1-colin.king@canonical.com

drivers/gpu/drm/tinydrm/st7586.c

@@ -172,7 +172,7 @@ static const struct drm_framebuffer_funcs st7586_fb_funcs = {
 	.dirty		= st7586_fb_dirty,
 };
 
-void st7586_pipe_enable(struct drm_simple_display_pipe *pipe,
+static void st7586_pipe_enable(struct drm_simple_display_pipe *pipe,
 			       struct drm_crtc_state *crtc_state)
 {
 	struct tinydrm_device *tdev = pipe_to_tinydrm(pipe);