mic_virtio: fix a timeout loop

After the loop we test "if (!retry)" to see if we timedout.  The problem
is "retry--" is a post-op so retry will be -1 at the end of the loop.  I
have fixed this by changing it to a pre-op instead.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>