staging:rtl8192u: Remove unused extern DM_RxPathSelTable - Style

The file r8192U_dm.h defines the structure DM_RxPathSelTable as being
external. The structure is however declared in r8192U_dm.c and only
used locally in that file.

As a result the external definition has been removed and the declaration
in r8192U_dm.c changed to being of type static.

This is a coding style change which should not impact runtime code
execution.

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