pmdomain: mediatek: Fix power domain count

The wrong value of the number of domains is wrong which leads to
failures when trying to enumerate nested power domains.

 PM: genpd_xlate_onecell: invalid domain index 0
 PM: genpd_xlate_onecell: invalid domain index 1
 PM: genpd_xlate_onecell: invalid domain index 3
 PM: genpd_xlate_onecell: invalid domain index 4
 PM: genpd_xlate_onecell: invalid domain index 5
 PM: genpd_xlate_onecell: invalid domain index 13
 PM: genpd_xlate_onecell: invalid domain index 14

Attempts to use these power domains fail, so fix this by
using the correct value of calculated power domains.

Signed-off-by: Adam Ford <aford173@gmail.com>
Fixes: 88914db077b6 ("pmdomain: mediatek: Add support for Hardware Voter power domains")
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Cc: stable@vger.kernel.org
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>