Documentation/: fix warnings from -Wmissing-prototypes in HOSTCFLAGS

Fix up -Wmissing-prototypes in compileable userspace code, mainly under
Documentation/.

Signed-off-by: Ladinu Chandrasinghe <ladinu.pub@gmail.com>
Signed-off-by: Trevor Keith <tsrk@tsrk.net>
Cc: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/Documentation/video4linux/v4lgrab.c b/Documentation/video4linux/v4lgrab.c
index 05769cf..c8ded17 100644
--- a/Documentation/video4linux/v4lgrab.c
+++ b/Documentation/video4linux/v4lgrab.c
@@ -89,7 +89,7 @@
 	}                                                               \
 }
 
-int get_brightness_adj(unsigned char *image, long size, int *brightness) {
+static int get_brightness_adj(unsigned char *image, long size, int *brightness) {
   long i, tot = 0;
   for (i=0;i<size*3;i++)
     tot += image[i];