On some systems that actually have the bluetooth controller wired up
with an extra clock signal, it's possible the bluetooth controller
probes before the clock provider. clk_get would return a defer probe
error, which was not handled by this driver.

Handle this properly, so that these systems can work reliably.
Tested-by: Ondrej Jirman <megous@megous.com>
Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>