tests/test-char.c: Don't use main_loop_wait()'s return value

In QEMU's main_loop() we used to check whether we should do
a nonblocking call to main_loop(); this was deleted in commit e330c118,
because now that vCPUs always drop the I/O thread lock it is an unnecessary
optimization.

The loop in test-char.c copied the old QEMU main_loop() code, but
here the nonblocking check has never been necessary because this
standalone test case doesn't hold the I/O lock anyway. Remove it,
so we can drop the main_loop_wait() return value.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-Id: <1498584769-12439-2-git-send-email-peter.maydell@linaro.org>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>