dmaengine: ti: edma: Annotate struct edma_desc 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 edma_desc.

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

Cc: Vinod Koul <vkoul@kernel.org>
Cc: Peter Ujfalusi <peter.ujfalusi@gmail.com>
Cc: dmaengine@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: "Gustavo A. R. Silva" <gustavoars@kernel.org>
Link: https://lore.kernel.org/r/20230817235859.49846-17-keescook@chromium.orgSigned-off-by: Vinod Koul <vkoul@kernel.org>

drivers/dma/ti/edma.c

@@ -202,7 +202,7 @@ struct edma_desc {
 	u32				residue;
 	u32				residue_stat;
 
-	struct edma_pset		pset[];
+	struct edma_pset		pset[] __counted_by(pset_nr);
 };
 
 struct edma_cc;