ia64: Fix efi_mem_type() and efi_mem_attributes() to avoid potential

ia64: Fix efi_mem_type() and efi_mem_attributes() to avoid potential
	underflows.  In my case, the underflows occurred with the
	first memory descriptor which got trimmed down to a size of 0.
	Due to the underflow, this descriptor ended up covering the entire
	address-range which in turn caused Bad Things to happen with the
	X server.