Fix assignment of "num_planes" in vaapi allocator

Usually there are 2 planes for NV12 buffers during decoding, but
during encoding the RGBA source buffer has only a single plane.
Assign info.numOfPlanes instead to set the correct plane count.

Change-Id: I491268b39c0376645f643a27803a983e6511a043

omx_utils/src/mfx_omx_vaapi_allocator.cpp

@@ -517,7 +517,7 @@ mfxStatus MfxOmxVaapiFrameAllocator::CreateSurfaceFromGralloc(const mfxU8* handl
     surfExtBuf.width = width;
     surfExtBuf.height = height;
     surfExtBuf.pitches[0] = info.pitch;
-    surfExtBuf.num_planes = 2;
+    surfExtBuf.num_planes = info.numOfPlanes;
     surfExtBuf.num_buffers = 1;
 #ifdef MFX_OMX_USE_PRIME
     surfExtBuf.buffers = (uintptr_t *)&(info.prime);