can-bcm: fix minor heap overflow

commit 0597d1b99fcfc2c0eada09a698f85ed413d4ba84 upstream.

On 64-bit platforms the ASCII representation of a pointer may be up to 17
bytes long. This patch increases the length of the buffer accordingly.

http://marc.info/?l=linux-netdev&m=128872251418192&w=2

Reported-by: Dan Rosenberg <drosenberg@vsecurity.com>
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
CC: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>