rtio: remove padding field `_resv0` from `struct rtio_sqe` #153072

Job	Run time
twister-build-prep / prep_pr	2m 56s
twister-build-prep / prep_push	0s
twister-build (1)	25m 39s
twister-build (2)	36m 19s
twister-build (3)	30m 33s
twister-build (4)	34m 48s
twister-build (5)	29m 3s
twister-build (6)	20m 43s
twister-build (7)	23m 51s
Publish Unit Tests Results	10s
Check Twister Status / all jobs passed	1s
	3h 24m 3s

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