target/mips: Fix MSA MSUBV.B opcode

target/mips: Fix MSA MSUBV.B opcode

The result of the 'Vector Multiply and Subtract' opcode is
incorrect with Byte vectors. Probably due to a copy/paste error,
commit 5f148a02327 mistakenly used the $wt (target register)
instead  of $wd (destination register) as first operand. Fix that.

Cc: Aleksandar Rikalo <aleksandar.rikalo@syrmia.com>
Fixes: 5f148a02327 ("target/mips: msa: Split helpers for MSUBV.<B|H|W|D>")
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20211028210843.2120802-3-f4bug@amsat.org>