I suspect the question was not intended to be limited to hash paths of a specific depth. I'd suggest something like this:

sub hpath(\%$) {
    my ($href, $path) = @_;
    while ($path =~ /\G(.+?)\.?/gc) {
        $href = $href->{$1};
    }
    return $href;
}

my %c = (1 => { 2 => { 3 => 4 }});
print hpath(%c, "1.2.3");
[download]

Only with error checking, of course. Substitute while  ... with foreach (split(/\./, $path) (and $1 with $_) for slightly different flavor.