mips: Handle KCOV __init vs inline mismatch

mips: Handle KCOV __init vs inline mismatch

When KCOV is enabled all functions get instrumented, unless
the __no_sanitize_coverage attribute is used. To prepare for
__no_sanitize_coverage being applied to __init functions, we
have to handle differences in how GCC's inline optimizations get
resolved. For mips this requires adding the __init annotation on
init_mips_clocksource().

Reviewed-by: Huacai Chen <chenhuacai@loongson.cn>
Link: https://lore.kernel.org/r/20250717232519.2984886-9-kees@kernel.org
Signed-off-by: Kees Cook <kees@kernel.org>