[PATCH] b44: change comment about irq mask register

Through some experimentation with the similarly built bcm43xx I came to
the conclusion that if the hw/firmware sets a bit in the interrupt
register, an interrupt will only be raised if that bit is included in
the interrupt mask. Hence, the interrupt mask is more like an interrupt
control mask.

This patch changes the comment to reflect that.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Jeff Garzik <jeff@garzik.org>