msm: mdss: ignore pipe allocation error due to priority limitation

Pipe allocation can fail if the priority of the pipes in pair do not
satisfy the requirement. But these failures are not fatal and will be
handled in the next round. So ignore log spitting if pipe allocation
failure is due to priority limitation.

CRs-Fixed: 746386
Change-Id: I8586197a9653daa430617367e1e8ec3851d2cfa0
Signed-off-by: Ujwal Patel <ujwalp@codeaurora.org>