doc/filters: Fix vsbmc option name.

Reported-by: Антон Приходько

doc/filters.texi

@@ -9704,7 +9704,7 @@ Macroblock size. Default @code{16}.
 @item search_param
 Motion estimation search parameter. Default @code{32}.
 
-@item vsmbc
+@item vsbmc
 Enable variable-size block motion compensation. Motion estimation is applied with smaller block sizes at object boundaries in order to make the them less blur. Default is @code{0} (disabled).
 @end table
 @end table