Fix warnings in lwp/process.c

Fix warnings in lwp/process.c

 -- The EP/ep function does not return anything; declare the function pointer
    accordingly

 -- Explicitly cast &stackvar to char* to avoid a warning

Reviewed-on: http://gerrit.openafs.org/598
Tested-by: Derrick Brashear <shadow@dementia.org>
Reviewed-by: Derrick Brashear <shadow@dementia.org>