msm: mdss: fix panic signal support for RT interfaces

Wrong interface check in commit
2ab750c3 (support
danger safe signal per pipe) enables panic signal
for pipes connected to Non-RealTime(NRT) interfaces
instead of RealTime(RT). This inverts danger-safe
logic in MDSS driver. This change fixes the panic
signal support for RT interfaces.

Change-Id: If4bb363e312b25621b283a2dca429e88d14d5f84
Signed-off-by: Dhaval Patel <pdhaval@codeaurora.org>