[MIPS] ARC: Fix modpost warnings.

WARNING: vmlinux.o(.text+0x1608): Section mismatch: reference to .init.text:ArcRead (between 'indy_8254timer_irq' and 'indy_rtc_set_time')
WARNING: vmlinux.o(.text+0x1157ac): Section mismatch: reference to .init.text:ArcRead (between 'prom_getchar' and 'prom_putchar')
WARNING: vmlinux.o(.text+0x115808): Section mismatch: reference to .init.text:ArcWrite (between 'prom_putchar' and 'csum_partial')

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>