armv4: correct ARMV4 VERSTAGE guard

I overlooked the macro name change from the Kconfig option.
'ARM' and 'V4' should not be separated by a '_'.

Change-Id: I8bf0d851e6fd5b5cfc0aa29af2246540c8cb1399
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: http://review.coreboot.org/9371
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
1 file changed