[IA64] Fix perfmon sysctl directory modes

New sanity checks in sysctl_check_table() complain about a couple
of mode 0755 that should be 0555 in the perfmon code:

sysctl table check failed: /kernel .1 Writable sysctl directory
sysctl table check failed: /kernel/perfmon  Writable sysctl directory

Signed-off-by: Tony Luck <tony.luck@intel.com>