PCI: versatile: Remove redundant variable retval

PCI: versatile: Remove redundant variable retval

Variable retval is being assigned a value that is never read, the
variable is redundant and can be removed.

Cleans up clang scan build warning:
drivers/pci/controller/pci-versatile.c:37:10: warning: Although the value
stored to 'retval' is used in the enclosing expression, the value is never
actually read from 'retval' [deadcode.DeadStores]

Link: https://lore.kernel.org/r/20220418144416.86121-1-colin.i.king@gmail.com
Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>