MIPS: loongson64: cs5536: Fix PCI_OHCI_INT_REG reads

The PCI_OHCI_INT_REG case in pci_ohci_read_reg() contains the following
if statement:

  if ((lo & 0x00000f00) == CS5536_USB_INTR)

CS5536_USB_INTR expands to the constant 11, which gives us the following
condition which can never evaluate true:

  if ((lo & 0xf00) == 11)

At least when using GCC 8.1.0 this falls foul of the tautoligcal-compare
warning, and since the code is built with the -Werror flag the build
fails.

Fix this by shifting lo right by 8 bits in order to match the
corresponding PCI_OHCI_INT_REG case in pci_ohci_write_reg().

Signed-off-by: Paul Burton <paul.burton@mips.com>
Patchwork: https://patchwork.linux-mips.org/patch/19861/
Cc: Huacai Chen <chenhc@lemote.com>
Cc: James Hogan <jhogan@kernel.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org