x86/apic: Handle zero vector gracefully in clear_vector_irq()

x86/apic: Handle zero vector gracefully in clear_vector_irq()

If x86_vector_alloc_irq() fails x86_vector_free_irqs() is invoked to cleanup
the already allocated vectors. This subsequently calls clear_vector_irq().

The failed irq has no vector assigned, which triggers the BUG_ON(!vector) in
clear_vector_irq().

We cannot suppress the call to x86_vector_free_irqs() for the failed
interrupt, because the other data related to this irq must be cleaned up as
well. So calling clear_vector_irq() with vector == 0 is legitimate.

Remove the BUG_ON and return if vector is zero,

[ tglx: Massaged changelog ]

Fixes: b5dc8e6c21e7 "x86/irq: Use hierarchical irqdomain to manage CPU interrupt vectors"
Signed-off-by: Keith Busch <keith.busch@intel.com>
Cc: stable@vger.kernel.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
(cherry picked from commit 1bdb8970392a68489b469c3a330a1adb5ef61beb)

Orabug: 24515998,25975565

Signed-off-by: Ethan Zhao <ethan.zhao@oracle.com>
Reviewed-by: Yuval Shaia <yuval.shaia@oracle.com>
Reviewed-by: Jack Vogel <jack.vogel@oracle.com>
Conflicts:
	arch/x86/kernel/apic/vector.c