Fix build error: Indentation typo in cf-agent/Makefile.am

Since 4a6bd9384c7d563441e791759db11637b03ba948 I'm stuck on:

    Making all in cf-agent
    Makefile:884: *** missing separator.  Stop.
    Makefile:578: recipe for target 'all-recursive' failed
    make[1]: *** [all-recursive] Error 1
    Makefile:501: recipe for target 'all' failed
    make: *** [all] Error 2