target/i386: fix width of third operand of VINSERTx128

Table A-5 of the Intel manual incorrectly lists the third operand of
VINSERTx128 as Wqq, but it is actually a 128-bit value.  This is
visible when W is a memory operand close to the end of the page.

Fixes the recently-added poly1305_kunit test in linux-next.

(No testcase yet, but I plan to modify test-avx2 to use memory
close to the end of the page.  This would work because the test
vectors correctly have the memory operand as xmm2/m128).

Reported-by: Eric Biggers <ebiggers@kernel.org>
Tested-by: Eric Biggers <ebiggers@kernel.org>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: qemu-stable@nongnu.org
Fixes: 79068477686 ("target/i386: reimplement 0x0f 0x3a, add AVX", 2022-10-18)
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>