msm: camera: smmu: Fixes label_is_string warning in camera dtsi files

Property 'label' is a reserved property of type string. At present,
device trees use the property as list of strings.

Rename the property to 'cam-smmu-label' to resolve conflict.

CRs-Fixed: 2729703
Change-Id: I8bfb3af4daeaad4cc9dfc633a0256186ba1416c9
Signed-off-by: Anand Ravi <ananravi@codeaurora.org>