winmm: Standardize and simplify two error messages.

[Andrew Eikum]

On Wed, Jul 10, 2013 at 10:42:05AM +0200, Francois Gouget wrote:
> We don't have a MIDI Mapper configuration applet so don't tell the user to use it.
> ---
> 
> Or if we do, how does one get to it? I did not find anything in 
> winecfg.exe, nor in control.exe (the Control Panel).
> 
> -MIDIERR_NODEVICE, 		"The current MIDI Mapper setup refers to a MIDI device that is not installed on the system. Use MIDI Mapper to edit the setup."

I think it's meant to refer to the "MIDI Mapper" device, which is
configurable through the registry:
http://wiki.winehq.org/MIDI

I think your change is clearly an improvement.

Andrew