[brcm-2.4] fix wlcompat so that the wl module can be unloaded

[brcm-2.4] fix wlcompat so that the wl module can be unloaded

This patch was created on 8.09.2 but it also applies to Backfire
I found that I couldn't unload the broadcom wl driver, wlcompat didn't correctly release/decrement  the device pointer,
This patch cleans that up

I wanted to be able to remove/install the wl driver so that I could get out of monitor mode without rebooting

Signed-off-by: Chris Martin <chris@martin.cc>
git-svn-id: svn://svn.openwrt.org/openwrt/branches/backfire@25671 3c298f89-4303-0410-b956-a3cf2f4a3e73