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

[jovanbulck]

Current behavior erroneously jumps to the address of the BR instruction, instead of the SRC operand. This leads to an infinite loop as per below.

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EXAMPLE CODE (objdump)
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  7282:       30 40 68 73     br      #0x7368

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ORIGINAL BEHAVIOR
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*** STEP 0
block of len 4 at ip 0x7282
---- BEGIN VEX ----
IRSB {

   00 | ------ IMark(0x7282, 4, 0) ------
   01 | PUT(pc) = 0x7368
   NEXT: PUT(pc) = 0x7282; Ijk_Boring
}
---- END VEX ----

*** STEP 1
block of len 4 at ip 0x7282
...

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NEW BEHAVIOR
========================

*** STEP 0
block of len 4 at ip 0x7282
---- BEGIN VEX ----
IRSB {

   00 | ------ IMark(0x7282, 4, 0) ------
   01 | PUT(pc) = 0x7368
   NEXT: PUT(pc) = 0x7368; Ijk_Boring
}
---- END VEX ----

==== STEP 1
block of len 48 at ip 0x7368
...