genirq/test: Fail early if interrupt request fails

Requesting an interrupt is part of the basic test setup. If it fails, most
of the subsequent tests are likely to fail, and the output gets noisy.

Use "assert" to fail early.

Signed-off-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: David Gow <davidgow@google.com>
Link: https://lore.kernel.org/all/20250822190140.2154646-4-briannorris@chromium.org