file-hash-common: fix rule_file truncation

file-hash-common: fix rule_file truncation

Loading file hash lists uses dirname(3) on the
de_ctx->rule_file which modifies the contents,
removing the last part of the path. So on subsequent
calls the rule_file no longer contains the rule_file,
but instead just the directory name.

Mostly noticed when using "-S" with rule files outside
of the default-rule-path which requires more hunting for
the rule file.