spi: rzv2m-csi: Fix SoC product name

The SoC product name is "RZ/V2M".

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Fabrizio Castro <fabrizio.castro.jz@renesas.com>
Link: https://lore.kernel.org/r/89e9870a2c510387e4d7a863025f4d3639d4a261.1688375020.git.geert+renesas@glider.be


Signed-off-by: Mark Brown <broonie@kernel.org>