Input: ti_am335x_tsc - clamp coordinate_readouts to DT maximum (6)

Input: ti_am335x_tsc - clamp coordinate_readouts to DT maximum (6)

DT binding (ti,am3359-tsc.yaml) sets ti,coordinate-readouts to a
maximum of 6. The MFD parent also enforces that
(readouts * 2 + 2) + adc_channels <= 16 and fails probe if this
is violated, so the touchscreen subdriver will not even probe
in those cases.

Clamp coordinate_readouts > 6 to 6 in the subdriver to align with the
binding and keep behavior sane if invalid platform data bypasses schema
checks. Keep the existing default to 5 for non-positive values.

No functional change with valid DT.

Signed-off-by: Junjie Cao <junjie.cao@intel.com>
Link: https://patch.msgid.link/20251117032358.891822-1-junjie.cao@intel.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>