sws: Fix warning: ‘abase’ may be used uninitialized in this function

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libswscale/yuv2rgb.c

@@ -615,7 +615,7 @@ av_cold int ff_yuv2rgb_c_init_tables(SwsContext *c, const int inv_table[4], int
     uint8_t *y_table;
     uint16_t *y_table16;
     uint32_t *y_table32;
-    int i, base, rbase, gbase, bbase, abase, needAlpha;
+    int i, base, rbase, gbase, bbase, av_uninit(abase), needAlpha;
     const int yoffs = fullRange ? 384 : 326;
 
     int64_t crv =  inv_table[0];