mm: make early_pfn_to_nid() a C function

Fix this (sparc64)

mm/sparse-vmemmap.c: In function `vmemmap_verify':
mm/sparse-vmemmap.c:64: warning: unused variable `pfn'

by switching to a C function which touches its arg.

(reason 3,555 why macros are bad)

Also, the `nid' arg was misnamed.
Reviewed-by: Christoph Lameter <clameter@sgi.com>
Acked-by: Andy Whitcroft <apw@shadowen.org>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Andi Kleen <ak@suse.de>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/mmzone.h

@@ -841,7 +841,10 @@ static inline struct zoneref *first_zones_zonelist(struct zonelist *zonelist,
 
 #if !defined(CONFIG_HAVE_ARCH_EARLY_PFN_TO_NID) && \
 	!defined(CONFIG_ARCH_POPULATES_NODE_MAP)
-#define early_pfn_to_nid(nid)  (0UL)
+static inline unsigned long early_pfn_to_nid(unsigned long pfn)
+{
+	return 0;
+}
 #endif
 
 #ifdef CONFIG_FLATMEM