package/x11r7/xdriver_xf86-input-keyboard: Fix compile error

lnx_kbd.c: In function 'OpenKeyboard':
lnx_kbd.c:194:8: error: implicit declaration of function 'getpgid' [-Werror=implicit-function-declaration]
        rc = tcsetpgrp(pInfo->fd, getpgid(0));
        ^
lnx_kbd.c:194:8: warning: nested extern declaration of 'getpgid' [-Wnested-externs]
cc1: some warnings being treated as errors

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>