Some TDA998x variants (e.g. TDA19988) have an OSC_IN pin, to connect
an external oscillator circuit or clock source.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
---
This fixes "make dtbs_check":

    arch/arm64/boot/dts/renesas/r8a774c0-ek874-mipi-2.1.dtb: tda19988@70 (nxp,tda998x): Unevaluated properties are not allowed ('clocks' was unexpected)
	    from schema $id: http://devicetree.org/schemas/display/bridge/nxp,tda998x.yaml
    arch/arm64/boot/dts/renesas/r8a774c0-cat874.dtb: tda19988@70 (nxp,tda998x): Unevaluated properties are not allowed ('clocks' was unexpected)
	    from schema $id: http://devicetree.org/schemas/display/bridge/nxp,tda998x.yaml
    arch/arm64/boot/dts/renesas/r8a774c0-ek874.dtb: tda19988@70 (nxp,tda998x): Unevaluated properties are not allowed ('clocks' was unexpected)
	    from schema $id: http://devicetree.org/schemas/display/bridge/nxp,tda998x.yaml
    arch/arm64/boot/dts/renesas/r8a774c0-ek874-idk-2121wr.dtb: tda19988@70 (nxp,tda998x): Unevaluated properties are not allowed ('clocks' was unexpected)
	    from schema $id: http://devicetree.org/schemas/display/bridge/nxp,tda998x.yaml

This patch can be considered v3 of "[PATCH v2 2/3] [RFC] arm64: dts:
renesas: cat874: Drop bogus clocks property"[1], as the pin is actually
connected to a clock source on that board.  On BeagleBone Black, it is
also connected to a clock source, but not described in DT.

The linux driver does not use this clock directly, but I suspect[2] the
use of this pin is controlled through the AP_ENA register value, as
specified in the second cell of the the audio-ports property.

[1] https://lore.kernel.org/97b949cddd7e30e9c05873800330dccd3483b12b.1663165552.git.geert+renesas@glider.be (local)
[2] I do not have access to the programming manual.
---
 .../devicetree/bindings/display/bridge/nxp,tda998x.yaml        | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/Documentation/devicetree/bindings/display/bridge/nxp,tda998x.yaml b/Documentation/devicetree/bindings/display/bridge/nxp,tda998x.yaml
index 3fce9e698ea1d2dd..1205c8e9de329bbc 100644
--- a/Documentation/devicetree/bindings/display/bridge/nxp,tda998x.yaml
+++ b/Documentation/devicetree/bindings/display/bridge/nxp,tda998x.yaml

@@ -19,6 +19,9 @@ properties:
   interrupts:
     maxItems: 1
 
+  clocks:
+    maxItems: 1
+