wasapisink: fix regression in shared mode segment size

In commit fd806628a8 (839cc3926 in the stable branch) I changed the
segment size to match exactly the buffer size.  I missed that this is
only valid in exclusive mode and in shared mode the buffer size is
a multiple of the device period.

Revert the logic for the shared mode.

https://bugzilla.gnome.org/show_bug.cgi?id=796354

https://bugzilla.gnome.org/show_bug.cgi?id=796858
1 file changed