i2c: zx2967: use core helper to mark adapter suspended

Rejecting transfers should be handled by the core. Also, this will
ensure proper locking which was forgotten in this open coded version
and make sure resume mark is set after enabling clocks (not before).

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Acked-by: Shawn Guo <shawnguo@kernel.org>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>