pch_dma: Use GFP_ATOMIC because called from interrupt context

pdc_desc_get() is called from pd_prep_slave_sg, and the function is
called from interrupt context(e.g. Uart driver "pch_uart.c").
In fact, I saw kernel error message.
So, GFP_ATOMIC must be used not GFP_NOIO.

Signed-off-by: Tomoya MORINAGA <tomoya.rohm@gmail.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>