staging: rtl8192u: rework init and exit function

staging: rtl8192u: rework init and exit function

The init and exit functions are not releasing resource properly. An error
can be observed when we load/unload/load r8192u_usb module due to this
issue. This patch rework init and exit functions to do proper resource
release on init error and module unload.
The __exit attribute is stripped from some functions since they are now
being used by module init functions.

[  493.068012] proc_dir_entry 'net/ieee80211' already registered
[  493.271973]  proc_mkdir+0x18/0x20
[  493.272136]  ieee80211_debug_init+0x28/0xde8 [r8192u_usb]
[  493.272404]  rtl8192_usb_module_init+0x10/0x161 [r8192u_usb]

[   13.910616] proc_dir_entry 'net/rtl819xU' already registered
[   13.918931]  proc_mkdir+0x18/0x20
[   13.919098]  rtl8192_usb_module_init+0x142/0x16d [r8192u_usb]

Reviewed-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Tong Zhang <ztong0001@gmail.com>
Link: https://lore.kernel.org/r/20220224064033.1530924-3-ztong0001@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>