The &grab pointer we used to pass as userdata was the address of the function
argument which goes out of scope at the end of the function. This works fine
for devices immediately opened but when a device connects later, the address
may have been re-used since and it's content is undefined. If not NULL, we
end up grabbing the device.

Instead pass the grab option in which is guaranteed to live until the end of
main.

#26



Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
(cherry picked from commit 0a13223c)