staging: rtl8188eu: use table to get channel plan from country code

Use a table to get a channel plan from a given country code.This was a
TODO mentioned as a comment in the driver.

Signed-off-by: Hari Prasath Gujulan Elango <hgujulan@visteon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>