Fix nic lock usages around iwm_{read,write}_prph().

Fix nic lock usages around iwm_{read,write}_prph().

The iwm_{read,write}_prph() calls don't grab the nic lock themselves
so make sure to acquire it where necessary.
The iwm_{set,clear}_bits_prph() on the other hand acquire/release the
nic lock themselves. Since the nic lock doesn't do recursive locking
we need to be careful to avoid accidentally releasing the nic lock
too early that way.

Patch by Imre Vadasz.