msm: mdss: Fix assertive display HW range checks

Fix off by one error leading to log spam. 'nad_cfgs' is the upper bound of
the zero-indexed mixer/AD/dspp pipe enumeration.

Change-Id: I963d175aad23a8eb621772d6c9bd06676fa2e27e
Signed-off-by: Carl Vanderlip <carlv@codeaurora.org>
Signed-off-by: Ping Li <quicpingli@codeaurora.org>