staging: rtl8712: r8712_set_802_11_add_wep(): Change return values

staging: rtl8712: r8712_set_802_11_add_wep(): Change return values

Change call sites of r8712_set_802_11_add_wep to check for 0 and
non-zero values (e.g -EINVAL, -ENOMEM) instead of for _SUCCESS and
_FAIL.
Change return values of r8712_set_802_11_add_wep from true and false and
_SUCCESS to -EINVAL and the return value of r8712_set_key.
Change return type from u8 to int to accommodate these new return
values.

Signed-off-by: Nishka Dasgupta <nishkadg.linux@gmail.com>
Link: https://lore.kernel.org/r/20190722092341.21030-6-nishkadg.linux@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>