dmaengine: sprd: Annotate struct sprd_dma_dev with __counted_by

Prepare for the coming implementation by GCC and Clang of the __counted_by
attribute. Flexible array members annotated with __counted_by can have
their accesses bounds-checked at run-time checking via CONFIG_UBSAN_BOUNDS
(for array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
functions).

As found with Coccinelle[1], add __counted_by for struct sprd_dma_dev.

[1] https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci

Cc: Vinod Koul <[e-mail]>
Cc: Orson Zhai <[e-mail]>
Cc: Baolin Wang <[e-mail]>
Cc: Chunyan Zhang <[e-mail]>
Cc: [e-mail]
Signed-off-by: Kees Cook <[e-mail]>
Acked-by: Chunyan Zhang <[e-mail]>
Reviewed-by: "Gustavo A. R. Silva" <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Vinod Koul <[e-mail]>

drivers/dma/sprd-dma.c

···
 	struct clk		*ashb_clk;
 	int			irq;
 	u32			total_chns;
-	struct sprd_dma_chn	channels[];
+	struct sprd_dma_chn	channels[] __counted_by(total_chns);
 };
 
 static void sprd_dma_free_desc(struct virt_dma_desc *vd);