libkmod: _printf_format_ annotate and adjust ELFDBG modifiers

libkmod: _printf_format_ annotate and adjust ELFDBG modifiers

The recently added "always build ELFDBG" patch is already paying
dividends... Clang is flagging a "fmt" is not literal warning.

That's clearly wrong, although without _printf_format_ clang was
struggling to figure things out. With the attribute, it helpfully
flagged that handful of the modifiers are wrong.

Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Link: https://github.com/kmod-project/kmod/pull/172
Signed-off-by: Lucas De Marchi <lucas.de.marchi@gmail.com>