mfd: rz-mtu3: Reduce critical sections

mfd: rz-mtu3: Reduce critical sections

Reduce critical sections on rz_mtu3_start_stop_ch() and
rz_mtu3_is_enabled() by moving offset and bitpos computation
outside the critical section and drop the 'ret' variable on
rz_mtu3_is_enabled() and return 'tstr & BIT(bitpos)' directly.

Reported-by: Pavel Machek <pavel@denx.de>
Closes: https://lore.kernel.org/all/ZIMAse1ikTuycJ02@duo.ucw.cz/
Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Pavel Machek <pavel@denx.de>
Link: https://lore.kernel.org/r/20230815073445.9579-2-biju.das.jz@bp.renesas.com
Signed-off-by: Lee Jones <lee@kernel.org>