staging: rtl8192u: r8192U_core: fix unnecessary parentheses code style issue

Two sets of parentheses were used to contain the same statement.
In those cases, one of them has been removed, as unnecessary.

Signed-off-by: Raphaël Beamonte <raphael.beamonte@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>