configure: Fix enabling memalign_hack automatically

simd_align_16 is a configure item that can be enabled or disabled,
it's not a variable containing a list of other configure items
as need_memalign previously. This was broken in eba2233b5.

CC: libav-stable@libav.org
Signed-off-by: Martin Storsjö <martin@martin.st>
(cherry picked from commit 7813e6752b)
Signed-off-by: Luca Barbato <lu_zero@gentoo.org>

configure

@@ -4469,7 +4469,7 @@ enabled_all dxva2 CoTaskMemFree &&
     enable dxva2_lib
 
 ! enabled_any memalign posix_memalign aligned_malloc &&
-    enabled $simd_align_16 && enable memalign_hack
+    enabled simd_align_16 && enable memalign_hack
 
 map 'enabled $v && intrinsics=${v#intrinsics_}' $INTRINSICS_LIST