IB/mthca: Annotate struct mthca_icm_table 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 mthca_icm_table.

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

Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Leon Romanovsky <leon@kernel.org>
Cc: linux-rdma@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20230929180431.3005464-6-keescook@chromium.org
Signed-off-by: Leon Romanovsky <leon@kernel.org>

Author: kees

drivers/infiniband/hw/mthca/mthca_memfree.h

@@ -68,7 +68,7 @@ struct mthca_icm_table {
 	int               lowmem;
 	int               coherent;
 	struct mutex      mutex;
-	struct mthca_icm *icm[];
+	struct mthca_icm *icm[] __counted_by(num_icm);
 };
 
 struct mthca_icm_iter {