x86/hyperv: fix a warning in mshyperv.h

The following checkpatch warning is removed:
  WARNING: Use #include <linux/io.h> instead of <asm/io.h>

Signed-off-by: ZhiHu <huzhi001@208suo.com>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Signed-off-by: Wei Liu <wei.liu@kernel.org>