core: volume ramping fix

core: volume ramping fix

Hi,
I found that volume ramping is inside PA now.
there's a minor fix here, it is a bug i found after the patch is submitted:

line 1781 of sink-input.c :
if ((i->thread_info.ramp_info.envelope_dying - nbytes) <= 0) {
need to be changed to
if ((i->thread_info.ramp_info.envelope_dying - (ssize_t) nbytes) <= 0) {

otherwise this argument will never be negative since nbytes is of type
size_t which is unsigned.
Please change it when you have time, sorry if bring any inconvenience.  :)