isdn: divert: fix sprintf buffer overflow warning

One string we pass into the cs->info buffer might be too long,
as pointed out by gcc:

drivers/isdn/divert/isdn_divert.c: In function 'll_callback':
drivers/isdn/divert/isdn_divert.c:488:22: error: '%d' directive writing between 1 and 3 bytes into a region of size between 1 and 69 [-Werror=format-overflow=]
 sprintf(cs->info, "%d 0x%lx %s %s %s %s 0x%x 0x%x %d %d %s\n",
                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/isdn/divert/isdn_divert.c:488:22: note: directive argument in the range [0, 255]
drivers/isdn/divert/isdn_divert.c:488:4: note: 'sprintf' output 25 or more bytes (assuming 129) into a destination of size 90

This is unlikely to actually cause problems, so let's use snprintf
as a simple workaround to shut  up the warning and truncate the
buffer instead.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: David S. Miller <davem@davemloft.net>