PNP: remove pnp_mem_flags() as an lvalue

A future change will change pnp_mem_flags() from a "#define that
simplifies to an lvalue" to "an inline function that returns the
flags value."

Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
Acked-By: Rene Herman <rene.herman@gmail.com>
Signed-off-by: Len Brown <len.brown@intel.com>