staging: rtl8712: r8712_register_cmd_alive(): Change return values

Change return values of r8712_register_cmd_alive from _SUCCESS and _FAIL
to 0 and -EINVAL.
Change the return type of this function from sint to int.
Modify its call site to check for 0 instead of _SUCCESS.

Signed-off-by: Nishka Dasgupta <nishkadg.linux@gmail.com>
Link: https://lore.kernel.org/r/20190722092341.21030-4-nishkadg.linux@gmail.com


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