pipe3: Fix broken dependency

ARCH_OMAP2 has been renamed ARCH_OMAP2PLUS in commit a93fbf4a
("ARM: omap2+: rename config to ARCH_OMAP2PLUS and consolidate Kconfig")

Signed-off-by: Jean-Jacques Hiblot <jjhiblot@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>