mwifiex: rename mwifiex_free_adapter() routine in init.c

We have two different static routines with name
mwifiex_free_adapter(). The routine in main.c actually frees the
adapter structure.

We will rename other routine in init.c to mwifiex_adapter_cleanup()
to avoid confusion.

Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>