drivers:sensor:sensirion:scd4x: Fixed ID for power down command

[petrosyan-van]

SCD4X_CMD_POWER_DOWN should be 20 instead of 10.

The command to perform power down in SCD41 sensor is 0x36e0, which represents 20th element in scd4x_cmds array. The fix was tested with the actual sensor.

[github-actions]

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[yperess]

Verified on the data sheet, good catch.