TMS320: fix defects reported by coverity

** CID 1168318:  Dead default in switch  (DEADCODE)
/libr/asm/arch/tms320/tms320_dasm.c: 552 in get_mmm_str()

** CID 1168319:  Operands don't affect result  (CONSTANT_EXPRESSION_RESULT)
/libr/asm/arch/tms320/tms320_dasm.c: 383 in get_cond_str()
TMS320: fix invalid opcodes displaying

Now it show not only "invalid" string but the "invalid" string and the
opcode itself. Also, this patch fixes the problem with strange
instruction gap, that appears after the invalid opcode reveals.