codec/rfx: Fixed bufferpool size used for RemoteFX

y_r_buffer, cb_g_buffer, cr_b_buffer and dwt_buffer are all word arrays (16bit)
but obviously the bufferpool size was calculated based on the wrong assumption
that these are 32 bit values in commit 37a59efbe36c1e6dc200251e13492f20f63ff8b9
Merge pull request #1341 from nfedera/fix-2013-07-05-01

codec/rfx: Fixed bufferpool size used for RemoteFX