chroot: fix bashism

possible bashism in scripts/chroot.sh line 235 (should be 'b = a'):
	if [ "x${deb_arch}" == "xarmel" ] || [ "x${deb_arch}" == "xarmhf" ] ; then
possible bashism in scripts/chroot.sh line 238 (should be 'b = a'):
	if [ "x${deb_arch}" == "xarm64" ] ; then

fixes: https://github.com/RobertCNelson/omap-image-builder/issues/64



Signed-off-by: Robert Nelson <robertcnelson@gmail.com>