riscv: kexec_image: Fix dead link to boot-image-header.rst

Fix the reference to 'boot-image-header.rst', which was moved to
'Documentation/arch/riscv/' in commit 'ed843ae947'
("docs: move riscv under arch").

Signed-off-by: Soham Metha <sohammetha01@gmail.com>
Link: https://patch.msgid.link/20251203194355.63265-1-sohammetha01@gmail.com
Signed-off-by: Paul Walmsley <pjw@kernel.org>
This commit is contained in:
Soham Metha 2025-12-04 01:13:52 +05:30 • committed by Paul Walmsley
commit 938d79ec2b