usb: musb: da8xx: Call earlier clk_prepare_enable()

The first attempt to read a register may fail because the clock may not
be enabled, and then the probe of musb driver will fail.
Call clk_prepare_enable() before the first register read.

Signed-off-by: Alexandre Bailon <abailon@baylibre.com>
Signed-off-by: Bin Liu <b-liu@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>