ARC: fix reference of dependency for PAE40 config

Commit d71e629bed5b ("ARC: build: disallow invalid PAE40 + 4K page config")
reworks the build dependencies for ARC_HAS_PAE40, and accidentally refers
to the non-existing config option MMU_V4 rather than the intended option
ARC_MMU_V4. Note the missing prefix in the name here.

Refer to the intended config option in the dependency of the ARC_HAS_PAE40
config.

Fixes: d71e629bed5b ("ARC: build: disallow invalid PAE40 + 4K page config")
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@redhat.com>
Signed-off-by: Vineet Gupta <vgupta@kernel.org>