dmaengine: shdma: protect against the IRQ handler

The IRQ handler of the shdma driver accesses common hardware registers,
that are also accessed from other contexts. Therefore access to them
has to be performed with interrupts disabled, not only with disabled
bottom halves.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Vinod Koul <vinod.koul@linux.intel.com>