staging:rtl8192u: Remove HTHalfMcsToDataRate() - Style

The function HTHalfMcsToDataRate() is unused in code so has simply
been removed from the code.

As a result two static functions, (IsHTHalfNmode40Bandwidth and
IsHTHalfNmodeSGI), are not longer called, so they have been removed
as well.

These are coding style changes which should have no impact on
runtime code execution.

Signed-off-by: John Whitmore <johnfwhitmore@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>