vsnprintf: Drop unused const char fmt * in va_format()

vsnprintf: Drop unused const char fmt * in va_format()

va_format() doesn't use original formatting string, drop that
argument as it's done elsewhere in similar cases.

Suggested-by: Rasmus Villemoes <ravi@prevas.dk>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Kees Cook <kees@kernel.org>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20250321144822.324050-6-andriy.shevchenko@linux.intel.com
Signed-off-by: Petr Mladek <pmladek@suse.com>