soc: qcom: smem: Annotate struct qcom_smem 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 qcom_smem.

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

Cc: Andy Gross <agross@kernel.org>
Cc: Bjorn Andersson <andersson@kernel.org>
Cc: Konrad Dybcio <konrad.dybcio@linaro.org>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Tom Rix <trix@redhat.com>
Cc: linux-arm-msm@vger.kernel.org
Cc: llvm@lists.linux.dev
Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: "Gustavo A. R. Silva" <gustavoars@kernel.org>
Link: https://lore.kernel.org/r/20230922175413.work.929-kees@kernel.org
Signed-off-by: Bjorn Andersson <andersson@kernel.org>

drivers/soc/qcom/smem.c

@@ -285,7 +285,7 @@ struct qcom_smem {
 	struct smem_partition partitions[SMEM_HOST_COUNT];
 
 	unsigned num_regions;
-	struct smem_region regions[];
+	struct smem_region regions[] __counted_by(num_regions);
 };
 
 static void *