spi: sh-msiof: Document R-Car E3 support

Document support for the MSIOF module in the Renesas R-Car E3 (r8a77990)
SoC.

No driver update is needed.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Mark Brown <broonie@kernel.org>

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

@@ -12,6 +12,7 @@ Required properties:
 			 "renesas,msiof-r8a7795" (R-Car H3)
 			 "renesas,msiof-r8a7796" (R-Car M3-W)
 			 "renesas,msiof-r8a77965" (R-Car M3-N)
+			 "renesas,msiof-r8a77990" (R-Car E3)
 			 "renesas,msiof-r8a77995" (R-Car D3)
 			 "renesas,msiof-sh73a0" (SH-Mobile AG5)
 			 "renesas,sh-mobile-msiof" (generic SH-Mobile compatibile device)