kvm tools: fix repeated io emulation

When kvm emulates repeation io read instruction, it can exit to user-space with
'count' > 1, we need to emulate io access for many times

Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>