thermal/drivers/imx8mm: Suppress log message on probe deferral

nvmem_cell_read_u32() may return -EPROBE_DEFER if NVMEM supplier has not
yet been probed. Future reprobe may succeed, so printing:

  i.mx8mm_thermal 30260000.tmu: Failed to read OCOTP nvmem cell (-517).

to the log is confusing. Fix this by using dev_err_probe. This also
elevates the message from warning to error, which is more correct: The
log message is only ever printed in probe error path and probe aborts
afterwards, so it really warrants an error-level message.

Fixes: 40329164 ("thermal/drivers/imx: Add support for loading calibration data from OCOTP")
Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Reviewed-by: Marek Vasut <marex@denx.de>
Reviewed-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20230708112647.2897294-1-a.fatoum@pengutronix.de