dmaengine: use proper name for the R-Car SoC

It is 'R-Car', not 'r-car'. No code or binding changes, only descriptive text.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Acked-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>