alsa_sound: Fix a memory leak

A pointer variable was not being freed up which is
causing memory leak.
This change is to fix the same.

Change-Id: I12728a4a75fb303d34d10657fe9cbc1b55c1687e
CRs-Fixed: 523572
audio: fix for unhandled NULL pointer in HAL

- Check if handle is NULL before calling pcm_close
- Check if usecase is NULL before string comparison
  operations
- Disable unnecessary debug logs in HAL

Change-Id: I569cbf510c820e1a155abf3efb4bbb525e68aafb
alsa_sound: Fix for unhandled NULL pointer

-Passing NULL pointer to pcm_read()/pcm_write()/
 pcm_prepare() would crash, since it doesnt perform
 a NULL check before using the pointer, resulting
 in random crash
-Fix is to check whether handle is NULL or not.

Change-Id: I7061d40bddcaaae2145f5fc0a0229abeebead878
CRs-fixed: 549257