linux-user: Move target_to_host_errno_table[] setup out of ioctl loop

The code to initialise the target_to_host_errno_table[] array was
accidentally inside the loop through checking and initialising all
the supported ioctls. This was harmless but meant that we reinitialised the
array several hundred times on startup.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
