iwlwifi: cleanup usage of inline functions

Be consistent when using inline functions. If the function only used
once we move it to where it is used - no need for externs.

Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Cc: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>