arm64: dts: ti: Rename clock-names adc_tsc_fck to fck

Avoid the following warnings from dt-schema by just renaming the
clock-names string from adc_tsc_fck to fck so it matches the values in
ti,am3359-tscadc.yaml

tscadc@40200000: clock-names:0: 'fck' was expected

Signed-off-by: Matt Ranostay <mranostay@ti.com>
Signed-off-by: Nishanth Menon <nm@ti.com>
Tested-by: Judith Mendez <jm@ti.com>
Reviewed-by: Dhruva Gole <d-gole@ti.com>
Link: https://lore.kernel.org/r/20221024151648.394623-1-mranostay@ti.com