Fix condition for checking return value of play_sound()

Fix condition for checking return value of play_sound()

- Issue:
sttd_server_start() did not progress even though all behavior is
properly worked.

- Solution:
play_start_sound_for_uid() return true if start sound is playing.
However, previous code uses this return value reversely. So, the
sttd_server_start() worked inproperly.
To solve this issue, this patch fixes the condition properly. Through
this patch, sttd_server_start() will work properly.

Change-Id: Iba90d239b917182fbffea54cb526ebe5629262a7
Signed-off-by: Suyeon Hwang <stom.hwang@samsung.com>