defxx: Fix DEFPA enable error propagation

Correctly propagate the error code from `pci_enable_device' if non zero.
Currently a failure of this function is correctly recognized and device
initialization abandoned, however a successful completion code returned.

Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org>
Signed-off-by: David S. Miller <davem@davemloft.net>