Documentation: kunit: Clean up some string casts in examples

As the type checking is no longer excessively strict, get rid of the
unsightly (char*) casts -- and comment discussing them -- from the KUnit
usage page.

Signed-off-by: David Gow <[e-mail]>
Reviewed-by: Daniel Latypov <[e-mail]>
Acked-by: Brendan Higgins <[e-mail]>
Signed-off-by: Shuah Khan <[e-mail]>

Documentation/dev-tools/kunit/usage.rst

···
 
 .. code-block:: c
 
-	/* Note: the cast is to satisfy overly strict type-checking. */
 	#define TEST_SHA1(in, want) \
 		sha1sum(in, out); \
-		KUNIT_EXPECT_STREQ_MSG(test, (char *)out, want, "sha1sum(%s)", in);
+		KUNIT_EXPECT_STREQ_MSG(test, out, want, "sha1sum(%s)", in);
 
 	char out[40];
 	TEST_SHA1("hello world",  "2aae6c35c94fcfb415dbe95f408b9ce91ee846ed");
···
 	};
 	for (i = 0; i < ARRAY_SIZE(cases); ++i) {
 		sha1sum(cases[i].str, out);
-		KUNIT_EXPECT_STREQ_MSG(test, (char *)out, cases[i].sha1,
+		KUNIT_EXPECT_STREQ_MSG(test, out, cases[i].sha1,
 		                      "sha1sum(%s)", cases[i].str);
 	}
 
···
 		struct sha1_test_case *test_param = (struct sha1_test_case *)(test->param_value);
 
 		sha1sum(test_param->str, out);
-		KUNIT_EXPECT_STREQ_MSG(test, (char *)out, test_param->sha1,
+		KUNIT_EXPECT_STREQ_MSG(test, out, test_param->sha1,
 				      "sha1sum(%s)", test_param->str);
 	}