kprobes: use KSYM_NAME_LEN to size identifier buffers

Use KSYM_NAME_LEN to size identifier buffers, so that it can be easier
increased.

Signed-off-by: Joe Mario <jmario@redhat.com>
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>