iwlwifi: mvm: don't allocate BT_COEX cmd on stack

This command will change and be much bigger.
Prepare to that by stop allocating on the stack.

Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

diff --cc drivers/net/wireless/iwlwifi/mvm/bt-coex.c
Simple merge