wireless: cw1200: Use consistent internal locking conventions

The cw1200_irq_handler() function expects the hwbus lock to be held when
it is called.  On the SDIO platform, this lock is implemented in terms
of sdio_claim_host/sdio_release_host.

This trivial patch makes it explicit that we are performing the hwbus
lock rather than something SDIO-specific.

Signed-off-by: Solomon Peachy <pizza@shaftnet.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>