iwl3945: Remove DRV_NAME dependenies

As DRV_NAME is defined in 2 different header files, including both is not
possible.
This patch defines this constant from iwl3945-base.c and iwl-agn.c. It also
redefines the IWL_ERROR and IWL_WARNING macros to use dev_printk, as the
IWL_DEBUG_* macros do.

Signed-off-by: Samuel Ortiz <samuel.ortiz@intel.com>
Acked-by: Abhijeet Kolekar <abhijeet.kolekar@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>