staging: rtl8712: r8712_construct_txaggr_cmd_hdr(): Change return type

Change return type of r8712_construct_txaggr_cmd_hdr from u8 to void as
it always returns _SUCCESS and its return value is never used.

Signed-off-by: Nishka Dasgupta <nishkadg.linux@gmail.com>
Link: https://lore.kernel.org/r/20190809052353.5308-8-nishkadg.linux@gmail.com


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