mm/cma.c: suppress warning

mm/cma.c: In function 'cma_alloc':
mm/cma.c:366: warning: 'pfn' may be used uninitialized in this function

The patch actually improves the tracing a bit: if alloc_contig_range()
fails, tracing will display the offending pfn rather than -1.

Cc: Stefan Strogin <stefan.strogin@gmail.com>
Cc: Michal Nazarewicz <mpn@google.com>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Cc: Thierry Reding <treding@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/cma.c

@@ -363,7 +363,9 @@ err:
  */
 struct page *cma_alloc(struct cma *cma, size_t count, unsigned int align)
 {
-	unsigned long mask, offset, pfn, start = 0;
+	unsigned long mask, offset;
+	unsigned long pfn = -1;
+	unsigned long start = 0;
 	unsigned long bitmap_maxno, bitmap_no, bitmap_count;
 	struct page *page = NULL;
 	int ret;
@@ -418,7 +420,7 @@ struct page *cma_alloc(struct cma *cma, size_t count, unsigned int align)
 		start = bitmap_no + mask + 1;
 	}
 
-	trace_cma_alloc(page ? pfn : -1UL, page, count, align);
+	trace_cma_alloc(pfn, page, count, align);
 
 	pr_debug("%s(): returned %p\n", __func__, page);
 	return page;