mwifiex: cleanup in PCIe flr code path

adapter and card variables don't get freed during PCIe function level
reset. "adapter->ext_scan" variable need not be re-initialized.
fw_name and tx_buf_size initialization is moved to pcie specific code
so that mwifiex_reinit_sw() can be used by SDIO.

Signed-off-by: Xinming Hu <huxm@marvell.com>
Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>