counter: rz-mtu3-cnt: Reorder locking sequence for consistency

All functions except rz_mtu3_count_enable_write(), call
pm_runtime_{get,put} inside the lock. For consistency do the same here.

Reported-by: Pavel Machek <pavel@denx.de>
Closes: https://lore.kernel.org/r/ZH8Fmom8vZ4DwxqA@duo.ucw.cz
Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20230725154611.227556-1-biju.das.jz@bp.renesas.com/
Signed-off-by: William Breathitt Gray <william.gray@linaro.org>