Fixed bug 4277 - warnings patch

Sylvain

Patch a few warnings when using:
-Wmissing-prototypes -Wdocumentation -Wdocumentation-unknown-command

They are automatically enabled with -Wall

src/video/SDL_surface.c

@@ -37,7 +37,7 @@ SDL_COMPILE_TIME_ASSERT(surface_size_assumptions,
 /*
  * Calculate the pad-aligned scanline width of a surface
  */
-int
+static int
 SDL_CalculatePitch(Uint32 format, int width)
 {
     int pitch;