applypatch: Fix comparison of integers of different signs.

bootable/recovery/applypatch/imgpatch.cpp:57:3: error: comparison of integers of different signs: 'unsigned int' and 'int' [-Werror,-Wsign-compare]
  CHECK_GT(expected_target_length, 0);
  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

bootable/recovery/applypatch/freecache.cpp:145:50: error: comparison of integers of different signs: 'long' and '__fsblkcnt64_t' (aka 'unsigned long') [-Werror,-Wsign-compare]
  if (sf.f_bsize == 0 || free_space / sf.f_bsize != sf.f_bavail) {
                         ~~~~~~~~~~~~~~~~~~~~~~~ ^  ~~~~~~~~~~~
bootable/recovery/applypatch/freecache.cpp:190:16: error: comparison of integers of different signs: 'int64_t' (aka 'long') and 'size_t' (aka 'unsigned long') [-Werror,-Wsign-compare]
  if (free_now >= bytes_needed) {
      ~~~~~~~~ ^  ~~~~~~~~~~~~
bootable/recovery/applypatch/freecache.cpp:233:18: error: comparison of integers of different signs: 'int64_t' (aka 'long') and 'size_t' (aka 'unsigned long') [-Werror,-Wsign-compare]
    if (free_now >= bytes_needed) {
        ~~~~~~~~ ^  ~~~~~~~~~~~~

Test: `mmma -j bootable/recovery/applypatch` with -Wsign-compare
Test: Run recovery_unit_test on marlin.
Change-Id: I4aa1fd0f9b7205b9e4e50874fc4bccb62951e7fe