Staging: rtl8188eu: Combine two loops to increase readability

The first loop assigns values to ofdm_index array and the
second checks for boundary conditions. They are combined and
a comment is added to increase clarity.

Signed-off-by: Vatika Harlalka <vatikaharlalka@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>