Under CONFIG_OBU, there are a large number of duplicate lines for the
handling of INTER_FRAME and S_FRAME in the packing of the
uncompressed frame header. Indeed, there are only two lines of
difference between the handling of these two different frame types. By
removing the two lines, it has been confirmed the code between the two
"if" branches are completely identical.

Further, by unifying the handling of these two frame types, the
incorrect handling on S_FRAME under CONFIG_AMVR (default off) is fixed.

Change-Id: Iad5bb9704a871e61bcdb108223c6c6e131e341f2