irqdomain: Always associate interrupts for legacy domains

The unification of irq_domain_create_legacy() missed the fact that
interrupts must be associated even when the Linux interrupt number provided
in the first_irq argument is 0.

This breaks all call sites of irq_domain_create_legacy() which supply 0 as
the first_irq argument.

Enforce the association for legacy domains in __irq_domain_instantiate() to
cure this.

[ tglx: Massaged it slightly. ]

Fixes: 70114e7f ("irqdomain: Simplify simple and legacy domain creation")
Reported-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by Matti Vaittinen <mazziesaccount@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Link: https://lore.kernel.org/all/c3379142-10bc-4f14-b8ac-a46927aeac38@gmail.com