iio: dac: mcp4725: Fix i2c_master_send() return value handling

The i2c_master_send() returns number of sent bytes on success,
or negative on error. The suspend/resume callbacks expect zero
on success and non-zero on error. Adapt the return value of the
i2c_master_send() to the expectation of the suspend and resume
callbacks, including proper validation of the return value.

Fixes: cf35ad61

 ("iio: add mcp4725 I2C DAC driver")
Signed-off-by: Marek Vasut <marex@denx.de>
Reviewed-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Link: https://lore.kernel.org/r/20230511004330.206942-1-marex@denx.de


Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>