PCI: dwc: Print debug error message when MSI-X entry control mask bit is set

Add debug error message when MSI-X entry control mask bit is set, to help
debug the reason why a MSI-X interrupt is not being triggered.

Signed-off-by: Gustavo Pimentel <gustavo.pimentel@synopsys.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: Jingoo Han <jingoohan1@gmail.com>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Joao Pinto <joao.pinto@synopsys.com>