serial: mxs-auart: disable clks of Alphascale ASM9260

In case of Alphascale ASM9260 probe() enables s->clk and s->clk_ahb
via mxs_get_clks(), but there is no disable of the clocks.
The patch adds it to error paths and to mxs_auart_remove().

Found by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Fixes: 254da0d7 ("serial: mxs-auart: add Alphascale ASM9260 support")
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>