arm/gicv2m: Set errno when gicv2_update_routing() fails

In case of an error when updating the routing table entries,
irq__update_msix_route() uses perror to print an error message.
gicv2m_update_routing() doesn't set errno, and instead returns the value
that errno should have had, which can lead to failure messages like this:

KVM_SET_GSI_ROUTING: Success

Set errno in gicv2m_update_routing() to avoid such messages in the future.

Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com>
Link: https://lore.kernel.org/r/20211012132510.42134-2-alexandru.elisei@arm.com


Signed-off-by: Will Deacon <will@kernel.org>