PCI: Remove unused attr variable in pci_dma_configure

Clang warns:

drivers/pci/pci-driver.c:1603:21: error: unused variable 'attr'
[-Werror,-Wunused-variable]

Commit e5361ca2 ("ACPI / scan: Refactor _CCA enforcement") removed
attr's use and replaced it with its assigned value so it is no longer
needed.

Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>