serial: sh-sci: Drop support for "sci_ick" clock

Since commit 1b463bd5 ("ARM: dts: r8a7794: Rename the serial
port clock to fck") in v4.6, all upstream DTS files call the SCIF
functional clock "fck".

Hence the time is ripe to drop backward-compatibility with old DTBs that
use the old "sci_ick" name.

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/b4103e44d6ac46b6c1c264e2aeac80b39941fe74.1639663832.git.geert+renesas@glider.be


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>