bug: Hush suggest-attribute=format for __warn_printf()

bug: Hush suggest-attribute=format for __warn_printf()

Recent additions to this function cause GCC 14.3.0 to get excited
(W=1) and suggest a missing attribute:

	lib/bug.c: In function '__warn_printf':
	lib/bug.c:187:25: error: function '__warn_printf' be a candidate for 'gnu_printf' format attribute [-Werror=suggest-attribute=format]
	  187 |                         vprintk(fmt, *args);
	      |                         ^~~~~~~

Disable the diagnostic locally, following the pattern used for stuff
like va_format().

Fixes: 5c47b7f3d1a9 ("bug: Add BUG_FORMAT_ARGS infrastructure")
Signed-off-by: Brendan Jackman <jackmanb@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://patch.msgid.link/20251207-warn-printf-gcc-v1-1-b597d612b94b@google.com