x86: dma-mapping: fix broken allocation when dma_mask has been provided

Commit 0a2b9a6e ("X86: integrate CMA with DMA-mapping subsystem")
broke memory allocation with dma_mask. This patch fixes possible kernel
ops caused by lack of resetting page variable when jumping to 'again' label.
Reported-by: NKonrad Rzeszutek Wilk <konrad@darnok.org>
Signed-off-by: NMarek Szyprowski <m.szyprowski@samsung.com>
Acked-by: NMichal Nazarewicz <mina86@mina86.com>

arch/x86/kernel/pci-dma.c

@@ -100,7 +100,7 @@ void *dma_generic_alloc_coherent(struct device *dev, size_t size,
 				 struct dma_attrs *attrs)
 {
 	unsigned long dma_mask;
-	struct page *page = NULL;
+	struct page *page;
 	unsigned int count = PAGE_ALIGN(size) >> PAGE_SHIFT;
 	dma_addr_t addr;
 
@@ -108,6 +108,7 @@ void *dma_generic_alloc_coherent(struct device *dev, size_t size,
 
 	flag |= __GFP_ZERO;
 again:
+	page = NULL;
 	if (!(flag & GFP_ATOMIC))
 		page = dma_alloc_from_contiguous(dev, count, get_order(size));
 	if (!page)