mpegvideo.h has two function declarations with the 'inline' specifier

but no definition for those functions. The C standard requires a
definition to appear in the same translation unit for any function
declared with 'inline'. Most of the files including mpegvideo.h do not
define those functions. Fix this by removing the 'inline' specifiers
from the header.
patch by Uoti Urpala

Originally committed as revision 11830 to svn://svn.ffmpeg.org/ffmpeg/trunk