meson: fix machine option for x86_version

meson: fix machine option for x86_version

s/mbmi1/mbmi/

When configuring with -Dx86_version >= 3, meson step works, but
compilation fails because option -mbmi1 is unknown.

Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Tested-by: Alex Bennée <alex.bennee@linaro.org>
Link: https://lore.kernel.org/r/20241004223715.1275428-1-pierrick.bouvier@linaro.org
Cc: qemu-stable@nongnu.org
Fixes: ef7d1adfa85 ("meson: allow configuring the x86-64 baseline", 2024-06-28)
Revieved-by: Michael Tokarev <mjt@tls.msk.ru>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>