x86/kexec: Fix double-free of elf header buffer

In the Linux kernel, the following vulnerability has been resolved:

x86/kexec: Fix double-free of elf header buffer

After

b3e34a47f989 ("x86/kexec: fix memory leak of elf header buffer"),

freeing image->elf_headers in the error path of crash_load_segments()

is not needed because kimage_file_post_load_cleanup() will take

care of that later. And not clearing it could result in a double-free.

Drop the superfluous vfree() call at the error path of

crash_load_segments().