spi: sh-msiof: Match renesas,rx-fifo-size in DT bindings doc with driver

Commit fe78d0b7691c0274 ("spi: sh-msiof: Fix FIFO size to 64 word from
256 word") changed the default RX FIFO size on R-Car Gen2 SoCs in the
driver code, but forgot to update the DT bindings documentation.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/spi/sh-msiof.txt

@@ -51,7 +51,7 @@ Optional properties, deprecated for soctype-specific bindings:
 - renesas,tx-fifo-size : Overrides the default tx fifo size given in words
 			 (default is 64)
 - renesas,rx-fifo-size : Overrides the default rx fifo size given in words
-			 (default is 64, or 256 on R-Car Gen2)
+			 (default is 64)
 
 Pinctrl properties might be needed, too.  See
 Documentation/devicetree/bindings/pinctrl/renesas,*.