mjpegbdec: remove dead store

Signed-off-by: Paul B Mahol <onemda@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/mjpegbdec.c

@@ -129,7 +129,6 @@ read_header:
         if (s->bottom_field != s->interlace_polarity && second_field_offs)
         {
             buf_ptr = buf + second_field_offs;
-            second_field_offs = 0;
             goto read_header;
             }
     }