powerpc: If kexec_build_elf_info() fails return immediately from elf64_load()

Uninitialized local variable "elf_info" would be passed to
kexec_free_elf_info() if kexec_build_elf_info() returns an error
in elf64_load().

If kexec_build_elf_info() returns an error, return the error
immediately.

Signed-off-by: Lakshmi Ramasubramanian <nramas@linux.microsoft.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210421163610.23775-2-nramas@linux.microsoft.com