vp8: fix a bug in the internal PSNR calculation

While CONFIG_INTERNAL_STATS=1, PSNR is calculated while encoding.
The aligned width/height were used mistakenly in the calculation.
This patch fixed it, and used the orignal image width/height.

Change-Id: Iad5334f8693af761b71ebb78f2587db8a3404ecf
1 file changed