MIPS:DTS:Fix label name and interrupt number of ohci for Loongson-2K

from Loongson-2K1000 user manual know that under pci bus
the device num is 4, function number is 2 and register is 0x2200
is ohci. the ohci interrupt number is 51. because Loongson-2K1000 has
64 interrupt sources, 0-31 correspond to the device tree liointc0 device
 node, and the other correspond to liointc1 node. so it should be
number 19 correspon to liointc1.

Signed-off-by: xiaochuan mao <maoxiaochuan@loongson.cn>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>