[MIPS] Fix warning in mips-boards generic PCI

arch/mips/mips-boards/generic/pci.c: In function `mips_pcibios_init':
arch/mips/mips-boards/generic/pci.c:227: warning: comparison of distinct pointer types lacks a cast
arch/mips/mips-boards/generic/pci.c:228: warning: comparison of distinct pointer types lacks a cast

Signed-off-by: Yoichi Yuasa <yoichi_yuasa@tripeaks.co.jp>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>