Installd: Fix delete_code_cache() clearing the wrong cache dir

Fix a typo in delete_code_cache() introduced by commit c03de091, which
causes the function to empty /data/data/<package_name>/cache/ rather
than /data/data/<package_name>/code_cache/.

The following CTS test case should now pass:

 com.android.cts.appsecurity.SplitTests#testClearCodeCache

Change-Id: I2d9452d70ed39b3ea29ad65fb35e788c2fef5100
Signed-off-by: Hao Li <hao.i.li@intel.com>
Signed-off-by: Yu Ning <yu.ning@intel.com>