i2c: rcar: fixup rcar type naming

b720423a2627f045133bec39a31fe2bc0dab86f3
(i2c: rcar: add rcar-H2 support)
added R-Car H2 support on i2c-rcar.

The R-Car I2C type is based on SoC generation
(Gen1 = E1/M1/H1, Gen2 = E2/M2/H2),
but added naming was H1/H2 instead of Gen1/Gen2.
Gen1/Gen2 is better naming on this driver.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Acked-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>