firewire: test: Fix potential null dereference in firewire kunit test

kunit_kzalloc() may return a NULL pointer, dereferencing it without
NULL check may lead to NULL dereference.
Add a NULL check for test_state.

Fixes: 1c8506d ("firewire: test: add test of device attributes for simple AV/C device")
Signed-off-by: Charles Han <hanchunchao@inspur.com>
Link: https://lore.kernel.org/r/20250110084237.8877-1-hanchunchao@inspur.com
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>

Author: Charles Han

drivers/firewire/device-attribute-test.c

@@ -99,6 +99,7 @@ static void device_attr_simple_avc(struct kunit *test)
 	struct device *unit0_dev = (struct device *)&unit0.device;
 	static const int unit0_expected_ids[] = {0x00ffffff, 0x00ffffff, 0x0000a02d, 0x00010001};
 	char *buf = kunit_kzalloc(test, PAGE_SIZE, GFP_KERNEL);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, buf);
 	int ids[4] = {0, 0, 0, 0};
 
 	// Ensure associations for node and unit devices.
@@ -180,6 +181,7 @@ static void device_attr_legacy_avc(struct kunit *test)
 	struct device *unit0_dev = (struct device *)&unit0.device;
 	static const int unit0_expected_ids[] = {0x00012345, 0x00fedcba, 0x00abcdef, 0x00543210};
 	char *buf = kunit_kzalloc(test, PAGE_SIZE, GFP_KERNEL);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, buf);
 	int ids[4] = {0, 0, 0, 0};
 
 	// Ensure associations for node and unit devices.