MIPS: loongson32: ls1c: Fix hang during startup

The RTCCTRL reg of LS1C is obselete.
Writing this reg will cause system hang.

Fixes: 60219c56 ("MIPS: Add RTC support for Loongson1C board")
Signed-off-by: Yang Ling <gnaygnil@gmail.com>
Tested-by: Keguang Zhang <keguang.zhang@gmail.com>
Acked-by: Keguang Zhang <keguang.zhang@gmail.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>