staging:rtl8192u: Remove unused enum dm_dig_dbg_e - Style

The enumerated type dm_dig_dbg_e is never used in code so has simply
been removed from the source code.

this is a coding style change 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>