drivers/net/irda/irda-usb.c: fix buffer overflow

Taken from http://bugzilla.kernel.org/show_bug.cgi?id=12397

We're doing an sprintf of an 11-char string into an 11-char buffer.
Whoops.  It breaks firmware uploading.

Reported-by: Jos-Vicente Gilabert <josevteg@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>