Assert no mv clamping for scaled references

Assert no mv clamping for scaled references

Under --enable-better-hw-compabibility, this commit adds the asserts
that no mv clamping is applied for scaled references, so when built
with this configure option, decoder will assert if an input bitstream
triggger mv clamping for scaled reference frames.

Change-Id: I786e86a2bbbfb5bc2d2b706a31b0ffa8fe2eb0cb