Input: resistive-adc-touch - describe parameters in kernel doc

Input: resistive-adc-touch - describe parameters in kernel doc

Validation script is not happy:

 resistive-adc-touch.c:53: warning: Function parameter or member 'x_plate_ohms' not described in 'grts_state'
 resistive-adc-touch.c:53: warning: Function parameter or member 'ch' not described in 'grts_state'

Describe parameters in kernel doc to make it happy.

Fixes: fb082cd59afa ("Input: resistive-adc-touch - add support for z1 and z2 channels")
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20210528151113.85943-1-andriy.shevchenko@linux.intel.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>