iwl3945: use iwl_rx_mem_buffer

The patch replaces iwl3945_rx_mem_buffer with iwl_rx_mem_buffer.

Signed-off-by: Abhijeet Kolekar <abhijeet.kolekar@intel.com>
Signed-off-by: Zhu Yi <yi.zhu@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>