avcodec/xvmc: apply attribute_deprecated correctly

This fixes a warning observed on Clang 3.7:
"warning: attribute 'deprecated' is ignored, place it after "struct" to apply attribute to type declaration [-Wignored-attributes]"
and thus enables deprecation warning for the relevant struct.
Signed-off-by: Ganesh Ajjanagadde <gajjanagadde@gmail.com>
Signed-off-by: Ronald S. Bultje <rsbultje@gmail.com>

libavcodec/xvmc.h

@@ -43,7 +43,7 @@
 #define AV_XVMC_ID                    0x1DC711C0  /**< special value to ensure that regular pixel routines haven't corrupted the struct
                                                        the number is 1337 speak for the letters IDCT MCo (motion compensation) */
 
-attribute_deprecated struct xvmc_pix_fmt {
+struct attribute_deprecated xvmc_pix_fmt {
     /** The field contains the special constant value AV_XVMC_ID.
         It is used as a test that the application correctly uses the API,
         and that there is no corruption caused by pixel routines.