dmaengine: stm32-dma: fix potential race between pause and resume

When disabling dma channel, a TCF flag is set and as TCIE is enabled, an
interrupt is raised.
On a busy system, the interrupt may have latency and the user can ask for
dmaengine_resume while stm32-dma driver has not yet managed the complete
pause (backup of registers to restore state in resume).
To avoid such a case, instead of waiting the interrupt to backup the
registers, do it just after disabling the channel and discard Transfer
Complete interrupt in case the channel is paused.

Fixes: 099a9a94

 ("dmaengine: stm32-dma: add device_pause/device_resume support")
Signed-off-by: Amelie Delaunay <amelie.delaunay@foss.st.com>
Link: https://lore.kernel.org/r/20221024083611.132588-1-amelie.delaunay@foss.st.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>