PCI: spear: Use BUG_ON() instead of condition followed by BUG()

Use BUG_ON() instead of an if condition followed by BUG().

The semantic patch that makes this change is available in
scripts/coccinelle/misc/bugon.cocci.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
CC: Pratyush Anand <pratyush.anand@gmail.com>