net: ti: icssg-prueth: Stop hardcoding def_inc

net: ti: icssg-prueth: Stop hardcoding def_inc

The def_inc is stored in icss_iep structure. Currently default increment
(ns per clock tick) is hardcoded to 4 (Clock frequency being 250 MHz).
Change this to use the iep->def_inc variable as the iep structure is now
accessible to the driver files.

Reviewed-by: Roger Quadros <rogerq@kernel.org>
Signed-off-by: MD Danish Anwar <danishanwar@ti.com>
Link: https://patch.msgid.link/20240911081603.2521729-3-danishanwar@ti.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>