staging:rtl8192u: Remove enum dm_dig_op_e - Style

Remove the enumerated type dm_dig_op_e. The type is only used as a
parameter to the function dm_change_dynamic_initgain_thresh(), but
that function is never referenced in the code at all.

I would consider this to be a coding style change as the function is
never referenced and as a result the enumeration is never used. In
any case there should be no impact on runtime code execution.

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