dio: Fix buffer overflow in case of unknown board

With gcc 8.2.0:

    drivers/dio/dio.c: In function ‘dio_init’:
    drivers/dio/dio.c:240:17: warning: ‘strcpy’ writing 69 or more bytes into a region of size 64 overflows the destination [-Wstringop-overflow=]
		     strcpy(dev->name,dio_getname(dev->id));
		     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Indeed, if an unknown board is present, the target buffer will overflow.
Shorten the unknown board name string to fix this, and declare it as an
array while at it.
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>

drivers/dio/dio.c

@@ -89,8 +89,8 @@ static struct dioname names[] =
 #undef DIONAME
 #undef DIOFBNAME
 
-static const char *unknowndioname 
-        = "unknown DIO board -- please email <linux-m68k@lists.linux-m68k.org>!";
+static const char unknowndioname[]
+	= "unknown DIO board, please email linux-m68k@lists.linux-m68k.org";
 
 static const char *dio_getname(int id)
 {