msm: kgsl: Remove a warning at adreno_probe() time

The adreno driver uses the presence of iommu-secure-id property to
enable content protection. This property is a u32, and reading it as
a bool generated warnings at probe time. Read it as u32, and check
the return value to decide if it is enabled or disabled.

CRs-Fixed: 732302
Change-Id: I4aa533ab37e00fcef3b068f09f5a227076bfa787
Signed-off-by: Lynus Vaz <lvaz@codeaurora.org>