staging: rtlwifi: Remove unnecessary parentheses

Challenge suggested by coccinelle.
Remove unnecessary parentheses around the right hand side of an
assignment.

Signed-off-by: Payal Kshirsagar <payal.s.kshirsagar.98@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>