postgresql: set the tclsh as target path

The tclsh path in pltcl_listmod is set to sysroot, which causes pltcl_listmod
to fails to run on target, so fix the path to /usr/bin/tclsh.
    $ pltcl_listmod
    /usr/bin/pltcl_listmod: line 5: /buildarea1/WRLinux70-STD-0825/bitbake_build/tmp/sysroots/x86_64-linux/usr/bin/tclsh: No such file or directory
    $

Signed-off-by: Yue Tao <Yue.Tao@windriver.com>
Signed-off-by: Roy Li <rongqing.li@windriver.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>