[MIPS] Increase cp0 compare clockevent min_delta_ns from 0x30 to 0x300.

Extremly low values are of dubious usefulness anyway but in this case
they actually were killing Qemu which simply wasn't able to complete
mips_next_event() within 0x30 100MHz cycles even on fast hosts.

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