staging: rtl8723bs: core: Remove unnecessary parentheses

Removes unnecessary parentheses while returning an expression.Issue
found using coccinelle.
Semantic patch used to solve the problem is as follows:

@@
expression e;
@@

return
-(
e
-)
;

Signed-off-by: Vatsala Narang <vatsalanarang@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>