lib/test_printf.c: fix clang -Wformat warnings

see warnings:
| lib/test_printf.c:157:52: error: format specifies type 'unsigned char'
| but the argument has type 'int' [-Werror,-Wformat]
test("0|1|1|128|255",
| "%hhu|%hhu|%hhu|%hhu|%hhu", 0, 1, 257, 128, -1);
-
| lib/test_printf.c:158:55: error: format specifies type 'char' but the
| argument has type 'int' [-Werror,-Wformat] test("0|1|1|-128|-1",
| "%hhd|%hhd|%hhd|%hhd|%hhd", 0, 1, 257, 128, -1);
-
| lib/test_printf.c:159:41: error: format specifies type 'unsigned
short'
| but the argument has type 'int' [-Werror,-Wformat]
| test("2015122420151225", "%ho%ho%#ho", 1037, 5282, -11627);

There's an ongoing movement to eventually enable the -Wformat flag for
clang. Previous patches have targeted incorrect usage of
format specifiers. In this case, however, the "incorrect" format
specifiers are intrinsically part of the test cases. Hence, fixing them
would be misaligned with their intended purpose. My proposed fix is to
simply disable the warnings so that one day a clean build of the kernel
with clang (and -Wformat enabled) would be possible. It would also keep
us in the green for alot of the CI bots.

Link: https://github.com/ClangBuiltLinux/linux/issues/378


Suggested-by: Nathan Chancellor <nathan@kernel.org>
Suggested-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Justin Stitt <justinstitt@google.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20220718230626.1029318-1-justinstitt@google.com