sound/oss/opl3: Remove typedef opl_devinfo

This typedef is unnecessary and should just be removed as they are
never used.

The following Coccinelle semantic patch detects the case.

@tn@
identifier i;
type td;
@@

-typedef
 struct i { ... }
-td
 ;

@@
type tn.td;
identifier tn.i;
@@

-td
+ struct i

Signed-off-by: Himangi Saraogi <himangi774@gmail.com>
Acked-by: Julia Lawall <julia.lawall@lip6.fr>
Signed-off-by: Takashi Iwai <tiwai@suse.de>