video: ipu: prevent warnings with W=1

- make local functions static
- remove unused is_interlaced function

Signed-off-by: Jeroen Hofstee <jeroen@myspectrum.nl>
diff --git a/drivers/video/ipu_common.c b/drivers/video/ipu_common.c
index 8d4e925..5873531 100644
--- a/drivers/video/ipu_common.c
+++ b/drivers/video/ipu_common.c
@@ -379,7 +379,7 @@
 /*
  * This function resets IPU
  */
-void ipu_reset(void)
+static void ipu_reset(void)
 {
 	u32 *reg;
 	u32 value;