staging: rtl8712: r8712_xmit_classifier(): Change return values and type

Change return values of r8712_xmit_classifier from _SUCCESS and _FAIL to
0 and -EINVAL respectively.
Modify call site to check for non-zero return values instead of _FAIL.
Change return type from sint to int.

Signed-off-by: Nishka Dasgupta <nishkadg.linux@gmail.com>
Reviewed-by: Dan Carpenter <dan.carpenter@oracle.com>
Link: https://lore.kernel.org/r/20190808064012.12661-10-nishkadg.linux@gmail.com


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