[POWERPC] cell: Fix section mismatches in io-workarounds code

Fix following warnings:
WARNING: arch/powerpc/platforms/cell/built-in.o(.devinit.text+0x9c): Section mismatch in reference from the function .cell_setup_phb() to the function .init.text:.iowa_register_bus()
WARNING: arch/powerpc/platforms/cell/built-in.o(.devinit.text+0xa4): Section mismatch in reference from the function .cell_setup_phb() to the function .init.text:.io_workaround_init()

Signed-off-by: Kou Ishizaki <kou.ishizaki@toshiba.co.jp>
Signed-off-by: Paul Mackerras <paulus@samba.org>