Fix for out of bound access in lpd decode function

Code written under the condition
if (mod[0] == 0 && len_subfrm != LEN_FRAME) are redundant.
We were filling garbage at st->fd_synth[ORDER - len_subfrm + i]
and doing some calculations but never using it.

So removed the redundant part here.

Bug:122728400
Test: vendor + poc
Change-Id: If55eeec1e21b2874c1cfd8eee8c71dc7da962a72
1 file changed