s390/kdump: Fix memleak in nt_vmcoreinfo

[ Upstream commit 2d2e7075b87181ed0c675e4936e20bdadba02e1f ]

The vmcoreinfo of a crashed system is potentially fragmented. Thus the
crash kernel has an intermediate step where the vmcoreinfo is copied into a
temporary, continuous buffer in the crash kernel memory. This temporary
buffer is never freed. Free it now to prevent the memleak.

While at it replace all occurrences of "VMCOREINFO" by its corresponding
macro to prevent potential renaming issues.

Signed-off-by: Philipp Rudo <prudo@linux.ibm.com>
Acked-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>