clocksource/drivers/sh_cmt: Fix clocksource width for 32-bit machines

The driver seems to abuse *unsigned long* not only for the (32-bit)
register values but also for the 'sh_cmt_channel::total_cycles' which
needs to always be 64-bit -- as a result, the clocksource's mask is
needlessly clamped down to 32-bits on the 32-bit machines...

Fixes: 19bdc9d0

 ("clocksource: sh_cmt clocksource support")
Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>