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

Change return values of xmitframe_addmic from _SUCCESS and _FAIL to 0
and -ENOMEM respectively. Modify call sites to check for non-zero values
instead of _FAIL.
Also change return type from sint to int.

Signed-off-by: Nishka Dasgupta <nishkadg.linux@gmail.com>
Link: https://lore.kernel.org/r/20190813044638.16348-1-nishkadg.linux@gmail.com


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