avcodec/x86/dct-test: Use uint8_t for idct_simple_mmx_perm

The table contains no element outside the unsigned 8bit range
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/x86/dct-test.c

@@ -88,7 +88,7 @@ static const struct algo idct_tab_arch[] = {
     { 0 }
 };
 
-static const short idct_simple_mmx_perm[64] = {
+static const uint8_t idct_simple_mmx_perm[64] = {
     0x00, 0x08, 0x04, 0x09, 0x01, 0x0C, 0x05, 0x0D,
     0x10, 0x18, 0x14, 0x19, 0x11, 0x1C, 0x15, 0x1D,
     0x20, 0x28, 0x24, 0x29, 0x21, 0x2C, 0x25, 0x2D,