msp430: fix BR instruction behavior and register-indirect @Rn disassembly #57

Job	Run time
ci / Build	3m 3s
ci / Lint	46s
ci / Test (0)	1m 4s
ci / Test (1)	1m 2s
ci / Test (2)	1m 41s
ci / Test (3)	56s
ci / Test (4)	2m 9s
ci / Test (5)	55s
ci / Test (6)	59s
ci / Test (7)	1m 12s
ci / Test (8)	1m 41s
ci / Test (9)	1m 55s
ci / Publish Unit Tests Results	1s
	17m 24s

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