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 <[e-mail]>

drivers/dio/dio.c

···
 #undef DIONAME
 #undef DIOFBNAME
 
-static const char *unknowndioname 
-        = "unknown DIO board -- please email <[e-mail]>!";
+static const char unknowndioname[]
+	= "unknown DIO board, please email [e-mail]";
 
 static const char *dio_getname(int id)
 {