PCI: endpoint: pci-epf-vntb: Fix MSI doorbell IRQ unwind

PCI: endpoint: pci-epf-vntb: Fix MSI doorbell IRQ unwind

epf_ntb_db_bar_init_msi_doorbell() requests ntb->db_count doorbell IRQs
and then performs additional MSI doorbell setup that may still fail.
The error path unwinds the requested IRQs, but it uses a loop variable
that is reused later in the function. When a later step fails, the
unwind can run with an unexpected index value and leave some IRQs
requested.

Track the number of successfully requested IRQs separately and use that
counter for the unwind so all previously requested IRQs are freed on
failure.

Fixes: dc693d606644 ("PCI: endpoint: pci-epf-vntb: Add MSI doorbell support")
Signed-off-by: Koichiro Den <den@valinux.co.jp>
Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Reviewed-by: Niklas Cassel <cassel@kernel.org>
Link: https://patch.msgid.link/20260217063856.3759713-2-den@valinux.co.jp