clk: imx: replace osc_hdmi with dummy

There is no occurrence of the hdmi oscillator in the reference manual
(document IMX8MNRM Rev 2, 07/2022). Further, if we consider the indexes
76-81 and 134 of the "Clock Root" table of chapter 5 of the RM, there is
no entry for the source select bits 101b, which is the setting referenced
by "osc_hdmi".
Fix by renaming "osc_hdmi" with "dummy", a clock which has already been
used for missing source select bits.

Tested on the BSH SystemMaster (SMM) S2 board.

Fixes: 96d6392b ("clk: imx: Add support for i.MX8MN clock driver")
Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
Acked-by: Marco Felsch <m.felsch@pengutronix.de>
Signed-off-by: Abel Vesa <abel.vesa@linaro.org>
Link: https://lore.kernel.org/r/20221117113637.1978703-3-dario.binacchi@amarulasolutions.com