powerpc/powernv/pci: Fix underflow and leak issue

powerpc/powernv/pci: Fix underflow and leak issue

pnv_irq_domain_alloc() allocates interrupts at parent's interrupt
domain. If it fails in the progress, all allocated interrupts are
freed.

The number of successfully allocated interrupts so far is stored
"i". However, "i - 1" interrupts are freed. This is broken:

    - One interrupt is not be freed

    - If "i" is zero, "i - 1" wraps around

Correct the number of freed interrupts to "i".

Fixes: 0fcfe2247e75 ("powerpc/powernv/pci: Add MSI domains")
Signed-off-by: Nam Cao <namcao@linutronix.de>
Cc: stable@vger.kernel.org
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/70f8debe8688e0b467367db769b71c20146a836d.1754300646.git.namcao@linutronix.de