[IA64] fix IO_SPACE_SPARSE_ENCODING macro ambiguity
Parenthesize "p" to avoid ambiguity. No callers have a problem today;
this is just to clean up the bad form.
Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>