[media] omap: Fix typo "HAS_MMU"

Commit 38a07311 ("[media] omap: be sure that MMU is there for
COMPILE_TEST") added a dependency on HAS_MMU. There's no Kconfig symbol
HAS_MMU. Use MMU instead.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>