iwlwifi: don't WARN on host commands sent when firmware is dead

commit 8ca95995e64f5d270889badb3e449dca91106a2b upstream.

This triggers automatic bug reports and add no valuable
information. Print a simple error instead and drop the
host command.

Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>