wifi: iwlegacy: work around excessive stack usage on clang/kasan

In some rare randconfig builds, I seem to trigger a bug in clang where
it unrolls a loop but then runs out of registers, which then get
spilled to the stack:

net/wireless/intel/iwlegacy/4965-rs.c:2262:1: error: stack frame size (1696) exceeds limit (1280) in 'il4965_rs_rate_init' [-Werror,-Wframe-larger-than]

This seems to be the same one I saw in the omapdrm driver, and there is
an easy workaround by not inlining the il4965_rs_rate_scale_clear_win
function.

Link: llvm/llvm-project#143908
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Stanislaw Gruszka <stf_xl@wp.pl>
Link: https://patch.msgid.link/20250620113946.3987160-1-arnd@kernel.org
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

Author: arndb

drivers/net/wireless/intel/iwlegacy/4965-rs.c

@@ -203,7 +203,8 @@ il4965_rs_extract_rate(u32 rate_n_flags)
 	return (u8) (rate_n_flags & 0xFF);
 }
 
-static void
+/* noinline works around https://github.com/llvm/llvm-project/issues/143908 */
+static noinline_for_stack void
 il4965_rs_rate_scale_clear_win(struct il_rate_scale_data *win)
 {
 	win->data = 0;