dt-bindings: i2c: rcar: Rename bindings documentation file

Rename the bindings documentation file for R-Car I2C controller
from i2c-rcar.txt to renesas,i2c.txt.

This is part of an ongoing effort to name bindings documentation files for
Renesas IP blocks consistently, in line with the compat strings they
document.
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

MAINTAINERS

@@ -13650,7 +13650,7 @@ F:	drivers/iio/adc/rcar-gyroadc.c
 RENESAS R-CAR I2C DRIVERS
 M:	Wolfram Sang <wsa+renesas@sang-engineering.com>
 S:	Supported
-F:	Documentation/devicetree/bindings/i2c/i2c-rcar.txt
+F:	Documentation/devicetree/bindings/i2c/renesas,i2c.txt
 F:	Documentation/devicetree/bindings/i2c/renesas,iic.txt
 F:	drivers/i2c/busses/i2c-rcar.c
 F:	drivers/i2c/busses/i2c-sh_mobile.c