MAINTAINERS: Update git url for the wl1271 driver

We are integrating wl1271 commits via a new git tree now and wl1271
development should be made on top of the new tree.

Update the repository url accordingly.

Cc: John W. Linville <linville@tuxdriver.com>
Signed-off-by: Luciano Coelho <luciano.coelho@nokia.com>