xorg: bump X.org server version to 1.5.3

This version contains a fix to allow the compilation of the Xvesa
server against recent versions of the kernel headers (fix
http://cgit.freedesktop.org/xorg/xserver/commit/?h=server-1.5-branch&id=992a7168f0db5733fe4a6cbd2f40c6b1f2a150e0

)

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>