Use the function argument "name" instead of hardcoded
"VMCOREINFO". All callers use "VMCOREINFO" as argument, so this isn't
an exposed bug, thankfully.

Simplify a little bit the code while touching this.

Suggested-by: Andrew Jones <drjones@redhat.com>
Reported-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>