svga: avoid a calloc in svga_buffer_transfer_map()
svga: avoid a calloc in svga_buffer_transfer_map()

Just initialize the two other pipe_transfer fields explicitly.

Reviewed-by: Charmaine Lee <67ce69700661ea856134ddb10419a330e5f037d7@vmware.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler