The gpio field is not used anymore, remove the leftover.
This also fixes the compilation error after the ...

Fixes: 9855f05e ("ASoC: fsl: imx-es8328: Switch to using gpiod API")
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://msgid.link/r/20240325191341.3977321-1-andriy.shevchenko@linux.intel.comSigned-off-by: Mark Brown <broonie@kernel.org>