Mark switch cases where we are expecting to fall through.

This patch fixes the following warning (Building: bcm63xx_defconfig mips):

arch/mips/pci/ops-bcm63xx.c: In function ‘bcm63xx_pcie_can_access’:
arch/mips/pci/ops-bcm63xx.c:474:6: warning: this statement may fall through [-Wimplicit-fallthrough=]
   if (PCI_SLOT(devfn) == 0)
      ^
arch/mips/pci/ops-bcm63xx.c:477:2: note: here
  default:
  ^~~~~~~

Signed-off-by: Gustavo A. R. Silva <redacted>
---
 arch/mips/pci/ops-bcm63xx.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/mips/pci/ops-bcm63xx.c b/arch/mips/pci/ops-bcm63xx.c
index d02eb9d16b55..925c72348fb6 100644
--- a/arch/mips/pci/ops-bcm63xx.c
+++ b/arch/mips/pci/ops-bcm63xx.c

@@ -474,6 +474,7 @@ static int bcm63xx_pcie_can_access(struct pci_bus *bus, int devfn)
 		if (PCI_SLOT(devfn) == 0)
 			return bcm_pcie_readl(PCIE_DLSTATUS_REG)
 					& DLSTATUS_PHYLINKUP;
+		/* else, fall through */
 	default:
 		return false;
 	}

-- 
2.22.0