i2c: qup: use generic device property accessors

There's no reason for this driver to use OF-specific property helpers.
Drop the last one in favor of the generic variant and no longer include
of.h.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>