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>
2 files changed