memstick: jmb38x_ms: Annotate struct jmb38x_ms 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 jmb38x_ms.

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

Cc: Maxim Levitsky <maximlevitsky@gmail.com>
Cc: Alex Dubov <oakad@yahoo.com>
Cc: Ulf Hansson <ulf.hansson@linaro.org>
Cc: Tom Rix <trix@redhat.com>
Cc: Len Baker <len.baker@gmx.com>
Cc: Dan Carpenter <error27@gmail.com>
Cc: "Gustavo A. R. Silva" <gustavoars@kernel.org>
Cc: linux-mmc@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20230922175249.work.593-kees@kernel.orgSigned-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/memstick/host/jmb38x_ms.c

@@ -66,7 +66,7 @@ struct jmb38x_ms_host {
 struct jmb38x_ms {
 	struct pci_dev        *pdev;
 	int                   host_cnt;
-	struct memstick_host  *hosts[];
+	struct memstick_host  *hosts[] __counted_by(host_cnt);
 };
 
 #define BLOCK_COUNT_MASK       0xffff0000