irqchip/loongson-pch-msi: Fix off-by-one on allocation error path

When pch_msi_parent_domain_alloc() returns an error, there is an off-by-one
in the number of interrupts to be freed.

Fix it by passing the number of successfully allocated interrupts, instead of the
relative index of the last allocated one.

Fixes: 632dcc2c ("irqchip: Add Loongson PCH MSI controller")
Signed-off-by: Zenghui Yu <yuzenghui@huawei.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Link: https://lore.kernel.org/r/20240327142334.1098-1-yuzenghui@huawei.com