dmaengine: tegra210-adma: Annotate struct tegra_adma 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 tegra_adma.

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

Cc: Vinod Koul <vkoul@kernel.org>
Cc: Laxman Dewangan <ldewangan@nvidia.com>
Cc: Jon Hunter <jonathanh@nvidia.com>
Cc: Thierry Reding <thierry.reding@gmail.com>
Cc: dmaengine@vger.kernel.org
Cc: linux-tegra@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/20230817235859.49846-16-keescook@chromium.orgSigned-off-by: Vinod Koul <vkoul@kernel.org>

drivers/dma/tegra210-adma.c

@@ -162,7 +162,7 @@ struct tegra_adma {
 	const struct tegra_adma_chip_data *cdata;
 
 	/* Last member of the structure */
-	struct tegra_adma_chan		channels[];
+	struct tegra_adma_chan		channels[] __counted_by(nr_channels);
 };
 
 static inline void tdma_write(struct tegra_adma *tdma, u32 reg, u32 val)