string: kunit: add missing MODULE_DESCRIPTION() macros

make allmodconfig && make W=1 C=1 reports:
WARNING: modpost: missing MODULE_DESCRIPTION() in lib/string_kunit.o
WARNING: modpost: missing MODULE_DESCRIPTION() in lib/string_helpers_kunit.o

Add the missing invocation of the MODULE_DESCRIPTION() macro.
Signed-off-by: Jeff Johnson <quic_jjohnson@quicinc.com>
Link: https://lore.kernel.org/r/20240531-md-lib-string-v1-1-2738cf057d94@quicinc.comSigned-off-by: Kees Cook <kees@kernel.org>

lib/string_helpers_kunit.c

@@ -625,4 +625,5 @@ static struct kunit_suite string_helpers_test_suite = {
 
 kunit_test_suites(&string_helpers_test_suite);
 
+MODULE_DESCRIPTION("Test cases for string helpers module");
 MODULE_LICENSE("Dual BSD/GPL");

lib/string_kunit.c

@@ -633,4 +633,5 @@ static struct kunit_suite string_test_suite = {
 
 kunit_test_suites(&string_test_suite);
 
+MODULE_DESCRIPTION("Test cases for string functions");
 MODULE_LICENSE("GPL v2");