s390/qdio: increase string buffer size

Avoid false positive warnings like this with gcc 7.1:

drivers/s390/cio/qdio_debug.h:63:4:
 note: 'snprintf' output between 8 and 17 bytes into a destination of size 16
    snprintf(debug_buffer, QDIO_DBF_LEN, text);

and simply increase the size of the string buffer.
Reviewed-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

drivers/s390/cio/qdio_debug.h

@@ -11,7 +11,7 @@
 #include "qdio.h"
 
 /* that gives us 15 characters in the text event views */
-#define QDIO_DBF_LEN	16
+#define QDIO_DBF_LEN	32
 
 extern debug_info_t *qdio_dbf_setup;
 extern debug_info_t *qdio_dbf_error;