sf: Change log message in layer query method from ALOGE to ALOGW

This error can be seen for the following use case

1. Connect HDMI display
2. Dump the SurfaceFlinger state

The problem here is that HWComposer would have processed the display
connection event via the hotplug mechanism and considers that the
external display is connected. However, SurfaceFlinger has not
updated its internal state (mDisplays) since it will be waiting for
the mStateLock to be release by the dump function. As a result, when
the dump function invokes the getLayerSortedByZForHwcDisplay for the
external display, we will end up seeing the error log message because
SurfaceFlingers internal state has not yet been updated.

We can move this to ALOGW since it is a non-fatal/recoverable state.

CRs-Fixed: 914173
Change-Id: Ib0ba359ecd894dd463417ba57ba1f72c07b5833e