DLS: fix loop calculation for 16-bit

Support for 16-bit wavetables was added in AOSP CL 9013377
This loop calculation should have been updated
but was missed.
This CL updates DLS_StartVoice() to match WT_StartVoice().

Thanks to kyungmin.jun at LGE for reporting the bug
and suggesting the fix.

Bug: 204673472
Test: Play a Jet file with DLS loops. See bug for repo.
Test: atest JetPlayerTest
Change-Id: I98e73a93296d9af455a51c64c767eb1ac7a5eba6
1 file changed