staging: rtl8712: r8712_set_key(): Change return values

Change return values of r8712_set_key from _SUCCESS and _FAIL to 0 and
-ENOMEM or -EINVAL, as the case may require.
Modify return statements and return variable accordingly.
Change return type from sint to int.
As there is only one site where the return value is used, update that
call site according to the change in the return values.

Signed-off-by: Nishka Dasgupta <nishkadg.linux@gmail.com>
Link: https://lore.kernel.org/r/20190722092341.21030-3-nishkadg.linux@gmail.com


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