target/arm: Fix MTE0_ACTIVE

In 50244cc7 we updated mte_check_fail to match the ARM
pseudocode, using the correct EL to select the TCF field.
But we failed to update MTE0_ACTIVE the same way, which led
to g_assert_not_reached().

Cc: qemu-stable@nongnu.org
Buglink: https://bugs.launchpad.net/bugs/1907137


Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20201221204426.88514-1-richard.henderson@linaro.org
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>