libpayload: Fix missing prototype warning for Xinitscr()

Xinitscr is only used internally in PDCurses, unless XCURSES
is defined. This patch fixes a warning that is produced because
of that.

Change-Id: I211f75717276cf028e0b435f328d1687d3536eb7
Signed-off-by: Stefan Reinauer <reinauer@google.com>
Reviewed-on: http://review.coreboot.org/2907
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>

payloads/libpayload/curses/PDCurses-3.4/pdcurses/initscr.c

@@ -108,6 +108,9 @@ MOUSE_STATUS Mouse_status, pdc_mouse_status;
 extern RIPPEDOFFLINE linesripped[5];
 extern char linesrippedoff;
 
+#ifndef XCURSES
+static
+#endif
 WINDOW *Xinitscr(int argc, char *argv[])
 {
     int i;