apparmor: test: Use NULL macros

Replace the PTR_EQ NULL checks with the more idiomatic and specific NULL
macros.
Acked-by: NDaniel Latypov <dlatypov@google.com>
Signed-off-by: NRicardo Ribalda <ribalda@chromium.org>
Acked-by: NBrendan Higgins <brendanhiggins@google.com>
Signed-off-by: NShuah Khan <skhan@linuxfoundation.org>

security/apparmor/policy_unpack_test.c

@@ -313,7 +313,7 @@ static void policy_unpack_test_unpack_strdup_out_of_bounds(struct kunit *test)
 	size = unpack_strdup(puf->e, &string, TEST_STRING_NAME);
 
 	KUNIT_EXPECT_EQ(test, size, 0);
-	KUNIT_EXPECT_PTR_EQ(test, string, (char *)NULL);
+	KUNIT_EXPECT_NULL(test, string);
 	KUNIT_EXPECT_PTR_EQ(test, puf->e->pos, start);
 }
 
@@ -409,7 +409,7 @@ static void policy_unpack_test_unpack_u16_chunk_out_of_bounds_1(
 	size = unpack_u16_chunk(puf->e, &chunk);
 
 	KUNIT_EXPECT_EQ(test, size, (size_t)0);
-	KUNIT_EXPECT_PTR_EQ(test, chunk, (char *)NULL);
+	KUNIT_EXPECT_NULL(test, chunk);
 	KUNIT_EXPECT_PTR_EQ(test, puf->e->pos, puf->e->end - 1);
 }
 
@@ -431,7 +431,7 @@ static void policy_unpack_test_unpack_u16_chunk_out_of_bounds_2(
 	size = unpack_u16_chunk(puf->e, &chunk);
 
 	KUNIT_EXPECT_EQ(test, size, (size_t)0);
-	KUNIT_EXPECT_PTR_EQ(test, chunk, (char *)NULL);
+	KUNIT_EXPECT_NULL(test, chunk);
 	KUNIT_EXPECT_PTR_EQ(test, puf->e->pos, puf->e->start + TEST_U16_OFFSET);
 }