arch/ia64/kernel/mca_asm.S is treating per_cpu__ia64_mca_data as the
start of the mca data, instead of as a pointer to the mca data.  It
ends up overwriting the rest of the per cpu area with the MCA stack and
bspstore.  Since we dereference ia64_mca_data several times, make it a
macro.
Signed-off-by: Keith Owens <kaos@sgi.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>