Fix fsal_obj leak in cache_inode_lookupp_impl()

cache_inode_lookupp_impl() used to first call FSAL lookup() which creates a
fsal_obj, but then used cache_inode_get() with the parent key from the object
to get a cache entry. This caused a leak of the fsal_obj created by the
lookup() call which was never released.
A simpler and safer approach is to call cache_inode_new_entry() directly using
the fsal_obj created by lookup().

Signed-off-by: Amit Dror <amitd@infinidat.com>