tcg/s390x: Fix encoding of VRIc, VRSa, VRSc insns

tcg/s390x: Fix encoding of VRIc, VRSa, VRSc insns

While the format names the second vector register 'v3',
it is still in the second position (bits 12-15) and
the argument to RXB must match.

Example error:
 -   e7 00 00 10 2a 33       verllf  %v16,%v0,16
 +   e7 00 00 10 2c 33       verllf  %v16,%v16,16

Cc: qemu-stable@nongnu.org
Reported-by: Michael Tokarev <mjt@tls.msk.ru>
Fixes: 22cb37b4172 ("tcg/s390x: Implement vector shift operations")
Fixes: 79cada8693d ("tcg/s390x: Implement tcg_out_dup*_vec")
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2054
Reviewed-by: Thomas Huth <thuth@redhat.com>
Tested-by: Michael Tokarev <mjt@tls.msk.ru>
Message-Id: <20240117213646.159697-2-richard.henderson@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>