nvmet: pci-epf: Do not add an IRQ vector if not needed

The function nvmet_pci_epf_create_cq() always unconditionally calls
nvmet_pci_epf_add_irq_vector() to add an IRQ vector for a completion
queue. But this is not correct if the host requested the creation of a
completion queue for polling, without an IRQ vector specified (i.e. the
flag NVME_CQ_IRQ_ENABLED is not set).

Fix this by calling nvmet_pci_epf_add_irq_vector() and setting the queue
flag NVMET_PCI_EPF_Q_IRQ_ENABLED for the cq only if NVME_CQ_IRQ_ENABLED
is set. While at it, also fix the error path to add the missing removal
of the added IRQ vector if nvmet_cq_create() fails.

Fixes: 0faa0fe6 ("nvmet: New NVMe PCI endpoint function target driver")
Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Keith Busch <kbusch@kernel.org>