PCI: dwc: Fix msg_atu_index assignment

PCI: dwc: Fix msg_atu_index assignment

When dw_pcie_iatu_setup() configures outbound address translation for both
type PCIE_ATU_TYPE_MEM and PCIE_ATU_TYPE_IO, the iATU index to use is
incremented before calling dw_pcie_prog_outbound_atu().

However for msg_atu_index, the index is not incremented before use,
causing the iATU index to be the same as the last configured iATU index,
which means that it will incorrectly use the same iATU index that is
already in use, breaking outbound address translation.

In total there are three problems with this code:
-It assigns msg_atu_index the same index that was used for the last
 outbound address translation window, rather than incrementing the index
 before assignment.
-The index should only be incremented (and msg_atu_index assigned) if the
 use_atu_msg feature is actually requested/in use (pp->use_atu_msg is set).
-If the use_atu_msg feature is requested/in use, and there are no outbound
 iATUs available, the code should return an error, as otherwise when this
 this feature is used, it will use an iATU index that is out of bounds.

Fixes: e1a4ec1a9520 ("PCI: dwc: Add generic MSG TLP support for sending PME_Turn_Off when system suspend")
Signed-off-by: Niklas Cassel <cassel@kernel.org>
Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
Tested-by: Maciej W. Rozycki <macro@orcam.me.uk>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Hans Zhang <zhanghuabing@ecosda.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Reviewed-by: Shawn Lin <shawn.lin@rock-chips.com>
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260127151038.1484881-6-cassel@kernel.org