i2c: muxes: i2c-arb-gpio-challenge: Demote non-conformant kernel-doc headers

Fixes the following W=1 kernel build warning(s):

drivers/i2c/muxes/i2c-arb-gpio-challenge.c:43: warning: Function parameter or member 'muxc' not described in 'i2c_arbitrator_select'
drivers/i2c/muxes/i2c-arb-gpio-challenge.c:43: warning: Function parameter or member 'chan' not described in 'i2c_arbitrator_select'
drivers/i2c/muxes/i2c-arb-gpio-challenge.c:86: warning: Function parameter or member 'muxc' not described in 'i2c_arbitrator_deselect'
drivers/i2c/muxes/i2c-arb-gpio-challenge.c:86: warning: Function parameter or member 'chan' not described in 'i2c_arbitrator_deselect'

Signed-off-by: Lee Jones <[e-mail]>
Acked-by: Douglas Anderson <[e-mail]>
Acked-by: Peter Rosin <[e-mail]>
Signed-off-by: Wolfram Sang <[e-mail]>

drivers/i2c/muxes/i2c-arb-gpio-challenge.c

···
 };
 
 
-/**
+/*
  * i2c_arbitrator_select - claim the I2C bus
  *
  * Use the GPIO-based signalling protocol; return -EBUSY if we fail.
···
 	return -EBUSY;
 }
 
-/**
+/*
  * i2c_arbitrator_deselect - release the I2C bus
  *
  * Release the I2C bus using the GPIO-based signalling protocol.