genirq/test: Fix depth tests on architectures with NOREQUEST by default.

The new irq KUnit tests fail on some architectures (notably PowerPC and
32-bit ARM), as the request_irq() call fails due to the ARCH_IRQ_INIT_FLAGS
containing IRQ_NOREQUEST, yielding the following errors:

[10:17:45]     # irq_free_disabled_test: EXPECTATION FAILED at kernel/irq/irq_test.c:88
[10:17:45]     Expected ret == 0, but
[10:17:45]         ret == -22 (0xffffffffffffffea)
[10:17:45]     # irq_free_disabled_test: EXPECTATION FAILED at kernel/irq/irq_test.c:90
[10:17:45]     Expected desc->depth == 0, but
[10:17:45]         desc->depth == 1 (0x1)
[10:17:45]     # irq_free_disabled_test: EXPECTATION FAILED at kernel/irq/irq_test.c:93
[10:17:45]     Expected desc->depth == 1, but
[10:17:45]         desc->depth == 2 (0x2)

By clearing IRQ_NOREQUEST from the interrupt descriptor, these tests now
pass on ARM and PowerPC.

Fixes: 66067c3c ("genirq: Add kunit tests for depth counts")
Signed-off-by: David Gow <davidgow@google.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Tested-by: Brian Norris <briannorris@chromium.org>
Reviewed-by: Brian Norris <briannorris@chromium.org>
Link: https://lore.kernel.org/all/20250816094528.3560222-2-davidgow@google.com