clk: renesas: r8a77990: Add missing I2C7 clock

clk: renesas: r8a77990: Add missing I2C7 clock

When trying to use I2C7 on R-Car E3:

    renesas-cpg-mssr e6150000.clock-controller: Cannot get module clock 1003: -2
    i2c-rcar e6690000.i2c: failed to add to PM domain always-on: -2
    i2c-rcar: probe of e6690000.i2c failed with error -2

Unlike other R-Car Gen3 SoCs, R-Car E3 has more than 7 I2C bus
interfaces.  Add the forgotten module clock for the 8th instance to fix
this.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Stephen Boyd <sboyd@kernel.org>