[xcb/xsettings] Byte order byte is at address 0

Accoring to
    http://standards.freedesktop.org\
    	        /xsettings-spec/xsettings-spec-0.5.html
the byte order byte is address 0 (not 1).

Change-Id: I441084a7f24908dd8a504648bfc50ba2d486a586
Reviewed-by: Jørgen Lind <jorgen.lind@digia.com>