xf86-input-synaptics 1.3.0: fix CROSS COMPILE Badness

xf86-input-synaptics 1.3.0: fix CROSS COMPILE Badness

It was failing to compile that way:
  make[2]: Entering directory `.../work/i686-angstrom-linux/xf86-input-synaptics-1_1.3.0-r14.0/xf86-input-synaptics-1.3.0/tools'
    CC     synclient.o
    CC     syndaemon-syndaemon.o
  CROSS COMPILE Badness: /usr/include in INCLUDEPATH: /usr/include/xorg
So I grepped for /usr/include/xorg and found that:
  Makefile:sdkdir = /usr/include/xorg
  Makefile.in:sdkdir = @sdkdir@
So simply passing the right directory to sdkdir fixed the issue.

Signed-off-by: Denis 'GNUtoo' Carikli <GNUtoo@no-log.org>