init-dom0less: better snprintf checks

init-dom0less: better snprintf checks

snprintf returns the number of characters that would have been written
to the final string if enough space had been available. A return value
of size or more means that the output was truncated.

Add a check for that in init-dom0less.

Signed-off-by: Stefano Stabellini <stefano.stabellini@xilinx.com>
Reviewed-by: Michal Orzel <michal.orzel@arm.com>
Acked-by: Julien Grall <jgrall@amazon.com>