calao_usb_a9260_defconfig: lock to kernel 3.10.x

The calao defconfig fails to build with 3.11, so lock the kernel version
to the last version known to build.

For details, see:
http://jenkins.free-electrons.com/job/buildroot/config=calao_usb_a9260_defconfig/105



Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>