staging: rtl8712: remove unnecessary return variables

Remove variables that are only used to hold and return constants and
have the functions directly return the constants.

Issue found by coccinelle:
@@
local idexpression ret;
expression e;
@@

-ret =
+return
     e;
-return ret;

Signed-off-by: Wambui Karuga <wambui.karugax@gmail.com>
Link: https://lore.kernel.org/r/f61a0f036af24228c682c6b12c3a8e6cf6736185.1570918228.git.wambui.karugax@gmail.com


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