kunit: Annotate _MSG assertion variants with gnu printf specifiers

kunit: Annotate _MSG assertion variants with gnu printf specifiers

KUnit's assertion macros have variants which accept a printf format
string, to allow tests to specify a more detailed message on failure.
These (and the related KUNIT_FAIL() macro) ultimately wrap the
__kunit_do_failed_assertion() function, which accepted a printf format
specifier, but did not have the __printf attribute, so gcc couldn't warn
on incorrect agruments.

It turns out there were quite a few tests with such incorrect arguments.

Add the __printf() specifier now that we've fixed these errors, to
prevent them from recurring.

Suggested-by: Linus Torvalds <[email protected]>
Signed-off-by: David Gow <[email protected]>
Tested-by: Guenter Roeck <[email protected]>
Reviewed-by: Justin Stitt <[email protected]>
Signed-off-by: Shuah Khan <[email protected]>