iwlwifi: move lockdep assertion into DVM

The fact that the mutex must be held is an
implementation detail of DVM, but something
has to ensure that no two synchronous cmds
are submitted concurrently. Move the lockdep
assertion into the DVM-specific code, but
also make the transport abort if there are
two concurrently commands.

The assertion is much more useful though as
the transport check can only catch it when
it actually happens, while the assertion
makes sure it can't possibly happen.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>