as3645a: Use ams,input-max-microamp as documented in DT bindings

DT bindings document the property "ams,input-max-microamp" that limits the
chip's maximum input current. The driver and the DTS however used
"peak-current-limit" property. Fix this by using the property documented
in DT binding documentation.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Jacek Anaszewski <jacek.anaszewski@gmail.com>