iwlwifi: use request_module instead of _nowait

Since request_module_nowait() can't be backported
use request_module() instead -- we don't need the
asynchronous behaviour of request_module_nowait()
here since we're running in the firmware request
work struct.

Tested-by: Donald H Fry <donald.h.fry@intel.com>
Reviewed-by: Donald H Fry <donald.h.fry@intel.com>
Reviewed-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>