cifs: fix another memleak, in cifs_root_iget

cifs: fix another memleak, in cifs_root_iget

commit a7851ce73b9fdef53f251420e6883cf4f3766534 upstream.

cifs_root_iget allocates full_path through
cifs_build_path_to_root, but fails to kfree it upon
cifs_get_inode_info* failure.

Make all failure exit paths traverse clean up
handling at the end of the function.

Signed-off-by: Oskar Schirmer <oskar@scara.com>
Reviewed-by: Jesper Juhl <jj@chaosbits.net>
Signed-off-by: Steve French <sfrench@us.ibm.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>