serial: 8250_bcm2835aux: Suppress clk_get error on -EPROBE_DEFER

Suppress a gratuitous error message if devm_clk_get() returns
-EPROBE_DEFER.

Signed-off-by: Phil Elwell <phil@raspberrypi.org>
[lukas: extend commit message]
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Reviewed-by: Matthias Brugger <mbrugger@suse.com>
Reviewed-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Tested-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Link: https://lore.kernel.org/r/deafc13cdfd7a31c6a81b0db95adcd3599accc26.1579175223.git.lukas@wunner.de


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>