Fixed PR19120 by rearranging the list of modules to search in @cast().

Fixed PR19120 by rearranging the list of modules to search in @cast().

* tapset/linux/dentry.stp (fullpath_struct_path): Rearrange the list of
  modules to search for 'struct path' so that looking in "<linux/path.h>"
  comes last, so that RHEL5-era kernels don't make it that far. That
  include file doesn't exist on RHEL5-era kernels, which causes kbuild
  warnings.