clk: imx: gate2: Check if clock is enabled against cgr_val

Seems the logic here was wrong all along. For example, if
the cgr_val is 2 (0b10), the clk_gate2_reg_is_enabled would
report the clock as disabled. So check against cgr_val instead.

Signed-off-by: Abel Vesa <abel.vesa@nxp.com>
Reviewed-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>