Input: synaptics-rmi4 - remove EXPORT_SYMBOL_GPL for internal functions

those functions should not be used outside of rmi_core.ko.
There is no point in exporting them to the world.

It looks like rmi_read_pdt_entry() should be static too.

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>