[media] media: ti-vpe: cal: Fix unreachable code in enum_frame_interval

As reported, the current cal_enum_frameintervals() is confusing
and does not have the intended behavior.
Fix this by re-implementing to properly propagate the enum_frame_interval
request to the subdevice.

[mchehab@osg.samsung.com: remove a now bogus "ret = 0" statement]
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Reported-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
Signed-off-by: Benoit Parrot <bparrot@ti.com>

Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>