clib_file_index is 0 if it is not initialized result in
following assertion on deleteing the pci device.
vpp/src/vppinfra/file.h:122 (clib_file_del_by_index) assertion `! pool_is_free (um->file_pool, _e)' fails
This patch fixes the issue by initializing the clib_file_index to -1.
Change-Id: I51d23f18e7ccf3143a4765d05aafc1363a007737
Signed-off-by: Mohsin Kazmi <sykazmi@cisco.com>