Fixes some warnings

- Implicit decleared function
- Unused variable

Change-Id: Ia701e66682cb6788f0716a2ef7556ed07227f78f
Fix a bunch of small system/core bugs.

Missing frees in:
  adb/file_sync_client.c
  fastboot/fastboot.c
  libsparse/output_file.c

Missing closedirs in:
  adb/file_sync_service.c
  cpio/mkbootfs.c
  libcutils/dir_hash.c

Potential buffer overrun in:
  gpttool/gpttool.c

Incorrect NULL check in:
  libsparse/backed_block.c

Bug: https://code.google.com/p/android/issues/detail?id=61564
Change-Id: If97838a9e73a77aef7f416c31c237ce1fca4ce21