rt2x00: Wait up to one second on rt2800 for WPDMA to be ready

At least some devices need such a long time to inititalize WPDMA. This
only increases the maximum wait time and shouldn't affect devices that
have been working before.

Reported-by: Joshua Smith <jesmith@kaon.com>
Signed-off-by: Helmut Schaa <helmut.schaa@googlemail.com>
Signed-off-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>