smb: client: handle path separator of created SMB symlinks

Convert path separator to CIFS_DIR_SEP(cifs_sb) from symlink target
before sending it over the wire otherwise the created SMB symlink may
become innaccesible from server side.

Fixes: 514d793e ("smb: client: allow creating symlinks via reparse points")
Signed-off-by: Paulo Alcantara (Red Hat) <pc@manguebit.com>
Signed-off-by: Steve French <stfrench@microsoft.com>