staging: rtl8712: r8712_free_xmitbuf(): Change return type

Change return type of r8712_free_xmitbuf from int to void (and remove
its return values) as its return value is never used.

Signed-off-by: Nishka Dasgupta <nishkadg.linux@gmail.com>
Link: https://lore.kernel.org/r/20190809052353.5308-5-nishkadg.linux@gmail.com


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