target/mips: Fix DEXTRV_S.H DSP opcode

target/mips: Fix DEXTRV_S.H DSP opcode

While for the DEXTR_S.H opcode:

  "The shift argument is provided in the instruction."

For the DEXTRV_S.H opcode we have:

  "The five least-significant bits of register rs provide the
   shift argument, interpreted as a five-bit unsigned integer;
   the remaining bits in rs are ignored."

While 't1' contains the 'rs' register content (the shift value
for DEXTR_S.H), we need to load the value of 'rs' for DEXTRV_S.H.
We can directly use the v1_t TCG register which already contains
this shift value.

Fixes: b53371ed5d4 ("target-mips: Add ASE DSP accumulator instructions")
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20211013215652.1764551-1-f4bug@amsat.org>