staging: rtl8712: init_drv_sw(): Change return values

Change return values of init_drv_sw from _SUCCESS and _FAIL to 0 and
-ENOMEM. Change return type from u8 to int to allow this.
Add a return variable to streamline return of error codes of called
functions.
Modify call site to check for non-zero return value instead of _FAIL.

Signed-off-by: Nishka Dasgupta <nishkadg.linux@gmail.com>
Link: https://lore.kernel.org/r/20190808064012.12661-7-nishkadg.linux@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>