i2c: use proper name for the R-Car SoC

It is 'R-Car', not 'RCar'. No code or binding changes, only descriptive text.
Signed-off-by: NWolfram Sang <wsa+renesas@sang-engineering.com>
Acked-by: NGeert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: NWolfram Sang <wsa@the-dreams.de>

drivers/i2c/busses/i2c-rcar.c

 /*
- * Driver for the Renesas RCar I2C unit
+ * Driver for the Renesas R-Car I2C unit
  *
  * Copyright (C) 2014-15 Wolfram Sang <wsa@sang-engineering.com>
  * Copyright (C) 2011-2015 Renesas Electronics Corporation