drivers: dma: stm32: add null callback checking #211963

Job	Run time
twister-build-prep	5m 35s
twister-build (2)	23m 30s
twister-build (1)	27m 5s
twister-build (5)	15m 5s
twister-build (6)	15m 53s
twister-build (4)	27m 17s
twister-build (7)	21m 8s
twister-build (3)	18m 21s
Publish Unit Tests Results	1m 22s
Check Twister Status / all jobs passed	3s
twister-build-prep	7m 33s
twister-build (2)	19m 10s
twister-build (3)	17m 41s
twister-build (4)	27m 38s
twister-build (1)	29m 23s
twister-build (5)	17m 32s
twister-build (7)	18m 16s
twister-build (6)	15m 21s
Publish Unit Tests Results	3m 36s
Check Twister Status / all jobs passed	3s
	5h 11m 32s

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