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).