clk: sunxi-ng: h6: fix PWM gate/reset offset

Currently the register offset of the PWM bus gate in Allwinner H6 clock
driver is wrong.

Fix this issue.

Fixes: 542353ea ("clk: sunxi-ng: add support for the Allwinner H6 CCU")
Signed-off-by: Rongyi Chen <chenyi@tt-cool.com>
[Icenowy: refactor commit message]
Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
Signed-off-by: Chen-Yu Tsai <wens@csie.org>