PCI: dwc: Rename variable name from data to d on dw_pci_bottom_mask/unmask()

Rename variable from data to d to maintain consistency between driver
functions, such as dw_msi_mask_irq() and dw_msi_unmask_irq().

No functional change is intended.

Signed-off-by: Gustavo Pimentel <gustavo.pimentel@synopsys.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: Joao Pinto <jpinto@synopsys.com>
Cc: Jingoo Han <jingoohan1@gmail.com>