drivers/message/i2o/i2o_config.c: bound allocation

Fix a case where users can try to allocate arbitarily large amounts of
memory. 64K is overkill for a config request so apply an upper bound.

Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>