m68k: Correct CONFIG_MVME16x macro name in #endif comment

A comment in arch/m68k/kernel/head.S incorrectly refers to
CONFIG_MVME162 and CONFIG_MVME167 instead of CONFIG_MVME16x. Correct it.

Discovered while searching for CONFIG_* symbols referenced in code but
not defined in any Kconfig file.

Signed-off-by: Ethan Nelson-Moore <enelsonmoore@gmail.com>
Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>
Link: https://patch.msgid.link/20260609201211.173438-1-enelsonmoore@gmail.com
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>