staging: rtl8192u: Fix keyidx assignment within if condition

Refactor the if condition into nested conditionals to improve clarity.
The condition is currently in the form of (E1 && E2 && E3), where the
variable keyidx is assigned a value in E3.

Signed-off-by: Wang Jinchao <wangjinchao600@gmail.com>
Link: https://lore.kernel.org/r/ZKQ7tYa9I+PHgef/@fedora


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