x86/kexec: fix incorrect argument passed to kexec_dprintk()

x86/kexec: fix incorrect argument passed to kexec_dprintk()

kexec_dprintk() expects the last argument to be kbuf.memsz, but the actual
argument being passed is kbuf.bufsz.

Although these two values are currently equal, it is better to pass the
correct one, in case these two values become different in the future.

Link: https://lkml.kernel.org/r/20231220154105.215610-1-ytcoode@gmail.com
Signed-off-by: Yuntao Wang <ytcoode@gmail.com>
Cc: Baoquan He <bhe@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>