OMAPDSS: fix build when DEBUG_FS or DSS_DEBUG_SUPPORT disabled

If CONFIG_DEBUG_FS or CONFIG_OMAP2_DSS_DEBUG_SUPPORT is disabled, the
build fails:

drivers/video/omap2/dss/core.c:197:50: error: static declaration of
'dss_debugfs_create_file' follows non-static declaration
drivers/video/omap2/dss/dss.h:166:5: note: previous declaration of
'dss_debugfs_create_file' was here

This patch fixes the dummy dss_debugfs_create_file() so that the driver
builds.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>

drivers/video/omap2/dss/core.c

@@ -194,8 +194,7 @@ static inline int dss_initialize_debugfs(void)
 static inline void dss_uninitialize_debugfs(void)
 {
 }
-static inline int dss_debugfs_create_file(const char *name,
-		void (*write)(struct seq_file *))
+int dss_debugfs_create_file(const char *name, void (*write)(struct seq_file *))
 {
 	return 0;
 }