bash-completion: fix function name of enosys completion

bash-completion: fix function name of enosys completion

The function "_enosys_module" referenced by the completion setting on
the last line of "bash-completion/enosys" is not defined in the
current master.  As reported in Ref. [1], this causes the following
error on an attempt at argument completion for the "enosys" command:

  bash: _enosys_module: command not found

[1] https://www.reddit.com/r/Fedora/comments/1llmu0w/comment/n00y98k/

Also, the function "_waitpid_module" defined in
"bash-completion/enosys" overwrites another completion function of the
same name defined in "bash-completion/waitpid".  This patch renames
the function in "bash-completion/enosys" to the correct one,
"_enosys_module".