tools: hv: Check return value of poll call

Check return value of poll call and if it fails print error
to the system log. If errno is EINVAL then exit with non-zero
value otherwise continue the while loop and call poll again.

Signed-off-by: Tomas Hozza <thozza@redhat.com>
Acked-by:  K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>