clk: imx: scu: remove the calling of device_is_bound

The device_is_bound() is invisible to drivers when built as modules.
It's also not aimed to be used by drivers according to Greg K.H.
Let's remove it from clk-scu driver and find another way to do proper
driver loading sequence.

Cc: Shawn Guo <shawnguo@kernel.org>
Cc: Sascha Hauer <kernel@pengutronix.de>
Cc: Stephen Boyd <sboyd@kernel.org>
Fixes: 77d8f306 ("clk: imx: scu: add two cells binding support")
Reported-by: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
Signed-off-by: Dong Aisheng <aisheng.dong@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>