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()