alloc_and_init_dma_members does not affect the interrupt status and is
only called by auto_attach, which also does not affect the interrupt
status. auto_attach() also contains a call to comedi_alloc_devpriv()
which calls kzalloc with GFP_KERNEL flag. Thus, there seems to be no
danger that dma_alloc_coherent can be called with interrupts turned
off, and GFP_KERNEL can be used.