dma: contiguous: Make dma_contiguous_default_area static

Now that dev_get_cma_area() is no longer inline, we don't have any user
of dma_contiguous_default_area() outside of contiguous.c so we can make
it static.

Signed-off-by: Maxime Ripard <mripard@kernel.org>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Link: https://lore.kernel.org/r/20260331-dma-buf-heaps-as-modules-v4-3-e18fda504419@kernel.org

Author: mripard

include/linux/dma-map-ops.h

@@ -91,8 +91,6 @@ static inline void set_dma_ops(struct device *dev,
 #endif /* CONFIG_ARCH_HAS_DMA_OPS */
 
 #ifdef CONFIG_DMA_CMA
-extern struct cma *dma_contiguous_default_area;
-
 struct cma *dev_get_cma_area(struct device *dev);
 struct cma *dma_contiguous_get_area_by_idx(unsigned int idx);
 

kernel/dma/contiguous.c

@@ -83,7 +83,7 @@ struct cma *dma_contiguous_get_area_by_idx(unsigned int idx)
 }
 EXPORT_SYMBOL_GPL(dma_contiguous_get_area_by_idx);
 
-struct cma *dma_contiguous_default_area;
+static struct cma *dma_contiguous_default_area;
 
 /*
  * Default global CMA area size can be defined in kernel's .config.