ARM: allow unaligned buffer in fixed-point NEON FFT4

This function is called with only 8-byte alignment from
imdct for size 16.  The fft4 function is not called for
the larger FFT or MDCT sizes, so this has no impact on
typical uses.

Signed-off-by: Mans Rullgard <mans@mansr.com>

libavcodec/arm/fft_fixed_neon.S

@@ -75,9 +75,9 @@
 .endm
 
 function fft4_neon
-        vld1.16         {d0-d1},  [r0,:128]
+        vld1.16         {d0-d1},  [r0]
         fft4            d0,  d1,  d2,  d3
-        vst1.16         {d0-d1},  [r0,:128]
+        vst1.16         {d0-d1},  [r0]
         bx              lr
 endfunc