rtc: test: Fix invalid format specifier.

'days' is a s64 (from div_s64), and so should use a %lld specifier.

This was found by extending KUnit's assertion macros to use gcc's
__printf attribute.

Fixes: 1d1bb12a ("rtc: Improve performance of rtc_time64_to_tm(). Add tests.")
Signed-off-by: David Gow <davidgow@google.com>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: Justin Stitt <justinstitt@google.com>
Acked-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

drivers/rtc/lib_test.c

@@ -54,7 +54,7 @@ static void rtc_time64_to_tm_test_date_range(struct kunit *test)
 
 		days = div_s64(secs, 86400);
 
-		#define FAIL_MSG "%d/%02d/%02d (%2d) : %ld", \
+		#define FAIL_MSG "%d/%02d/%02d (%2d) : %lld", \
 			year, month, mday, yday, days
 
 		KUNIT_ASSERT_EQ_MSG(test, year - 1900, result.tm_year, FAIL_MSG);