sh: Kill off volatile silliness in sq_flush_range().

  CC      arch/sh/kernel/cpu/sh4/sq.o
arch/sh/kernel/cpu/sh4/sq.c: In function 'sq_flush_range':
arch/sh/kernel/cpu/sh4/sq.c:65: warning: passing argument 1 of 'prefetch' discards qualifiers from pointer target type

This didn't actually need to be volatile in the first place, so just
kill off the qualifier entirely.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>