Fix integer sanitizer in audio_route_update_path.

Calculating i could sometimes cause an unsigned integer overflow, which
led to runtime errors on integer sanitized builds.

 runtime error: unsigned integer overflow: 0 - 1 cannot be represented in
 type 'unsigned int'

This refactors the loop to avoid the overflow.

Bug: 30969751
Test: Compiles and device boots.
Change-Id: I468d064eda5213fd773a094412cd669fc23617dc
Merged-In: I468d064eda5213fd773a094412cd669fc23617dc
1 file changed