irqchip/armada-370-xp: Fix support for Multi-MSI interrupts

irq-armada-370-xp driver already sets MSI_FLAG_MULTI_PCI_MSI flag into
msi_domain_info structure. But allocated interrupt numbers for Multi-MSI
needs to be properly aligned otherwise devices send MSI interrupt with
wrong number.

Fix this issue by using function bitmap_find_free_region() instead of
bitmap_find_next_zero_area() to allocate aligned interrupt numbers.

Signed-off-by: Pali Rohár <pali@kernel.org>
Fixes: a71b9412

 ("irqchip/armada-370-xp: Allow allocation of multiple MSIs")
Cc: stable@vger.kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20211125130057.26705-2-pali@kernel.org