dmaengine: fsl-edma: Annotate struct struct fsl_edma_engine 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 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 struct fsl_edma_engine.

Cc: Vinod Koul <vkoul@kernel.org>
Cc: dmaengine@vger.kernel.org
Link: https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci [1]
Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: "Gustavo A. R. Silva" <gustavoars@kernel.org>
Link: https://lore.kernel.org/r/20231003232704.work.596-kees@kernel.orgSigned-off-by: Vinod Koul <vkoul@kernel.org>

drivers/dma/fsl-edma-common.h

@@ -213,7 +213,7 @@ struct fsl_edma_engine {
 	bool			big_endian;
 	struct edma_regs	regs;
 	u64			chan_masked;
-	struct fsl_edma_chan	chans[];
+	struct fsl_edma_chan	chans[] __counted_by(n_chans);
 };
 
 #define edma_read_tcdreg(chan, __name)				\