clk: lan966x: Fix the lan966x clock gate register address

The register address used for the clock gate register is the base
register address coming from first reg map (ie. the generic
clock registers) instead of the second reg map defining the clock
gate register.

Use the correct clock gate register address.

Fixes: 5ad5915d

 ("clk: lan966x: Extend lan966x clock driver for clock gating support")
Signed-off-by: Herve Codina <herve.codina@bootlin.com>
Link: https://lore.kernel.org/r/20220704102845.168438-2-herve.codina@bootlin.com
Reviewed-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Tested-by: Michael Walle <michael@walle.cc>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>