fix: add missing tab and remove useless value assign

Author: newborn22

src/cmd/asm/internal/asm/testdata/riscv64.s

@@ -246,7 +246,7 @@ start:
 
 	// 15: Wait-on-Reservation-Set Instructions (Zawrs)
 	WRSNTO                              // 7300d000
-    WRSSTO                              // 7300d001
+	WRSSTO                              // 7300d001
 
 	// 20.5: Single-Precision Load and Store Instructions
 	FLW	(X5), F0				// 07a00200

src/cmd/internal/obj/riscv/obj.go

@@ -3615,7 +3615,7 @@ func instructionsForProg(p *obj.Prog) []*instruction {
 		ins.rd, ins.rs1, ins.rs2 = uint32(p.RegTo2), uint32(p.To.Reg), uint32(p.From.Reg)
 
 	case AWRSNTO, AWRSSTO:
-		ins.rd, ins.rs1, ins.imm = REG_ZERO, REG_ZERO, encode(p.As).csr
+		ins.rd, ins.rs1 = REG_ZERO, REG_ZERO
 
 	case AECALL, AEBREAK:
 		insEnc := encode(p.As)