i3c: master: cdns: Annotate struct cdns_i3c_xfer 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 cdns_i3c_xfer.

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

Cc: "Przemysław Gaj" <[e-mail]>
Cc: Alexandre Belloni <[e-mail]>
Cc: [e-mail]
Signed-off-by: Kees Cook <[e-mail]>
Reviewed-by: Gustavo A. R. Silva <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Alexandre Belloni <[e-mail]>

drivers/i3c/master/i3c-master-cdns.c

···
 	struct completion comp;
 	int ret;
 	unsigned int ncmds;
-	struct cdns_i3c_cmd cmds[];
+	struct cdns_i3c_cmd cmds[] __counted_by(ncmds);
 };
 
 struct cdns_i3c_data {