arm/armasm: fix wrong register order in MLA.S

Though "0xe0243192" can be correctly disassembled to
"MLA R1, R2, R3, R4", "0xe0243192" is disassembled to
"MLA.S R3, R1, R2, R4", which should be "MLA.S R1, R2, R3, R4".

This patch fix it.

fix golang/go#20752

Change-Id: I2b4627b822715954923429688bccb21c081b7d0e
Reviewed-on: https://go-review.googlesource.com/46456
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

arm/armasm/plan9x.go

@@ -115,7 +115,7 @@ func GoSyntax(inst Inst, pc uint64, symname func(uint64) (string, uint64), text
 	}
 	// For MLA-like instructions, the addend is the third operand.
 	switch inst.Op &^ 15 {
-	case SMLAWT_EQ, SMLAWB_EQ, MLA_EQ, MLS_EQ, SMMLA_EQ, SMMLS_EQ, SMLABB_EQ:
+	case SMLAWT_EQ, SMLAWB_EQ, MLA_EQ, MLA_S_EQ, MLS_EQ, SMMLA_EQ, SMMLS_EQ, SMLABB_EQ:
 		args = []string{args[1], args[2], args[0], args[3]}
 	}
 

arm/armasm/testdata/decode.txt

@@ -306,4 +306,5 @@ ff818c71|	1	gnu	strdvc r8, [ip, pc]
 |97acd647	1	gnu	error: unknown instruction
 ed003be9|	1	plan9	LDMDB [R0,R2-R3,R5-R7], R11!
 923124e0|	1	plan9	MLA R1, R2, R3, R4
+923134e0|	1	plan9	MLA.S R1, R2, R3, R4
 923164e0|	1	plan9	MLS R1, R2, R3, R4