dsp/lossless_enc.c: clear int sanitizer warnings

add explicit casts in calls to ColorTransformDelta()

clears warnings of the form:
implicit conversion from type 'uint8_t' (aka 'unsigned char') of value
254 (8-bit, unsigned) to type 'int8_t' (aka 'signed char') changed the
value to -2 (8-bit, signed)

Bug: b/229626362
Change-Id: I40618209509508f56d8053f9daa29cf2e6999766

src/dsp/lossless_enc.c

@@ -547,10 +547,10 @@ void VP8LTransformColor_C(const VP8LMultipliers* const m, uint32_t* data,
     const int8_t red   = U32ToS8(argb >> 16);
     int new_red = red & 0xff;
     int new_blue = argb & 0xff;
-    new_red -= ColorTransformDelta(m->green_to_red_, green);
+    new_red -= ColorTransformDelta((int8_t)m->green_to_red_, green);
     new_red &= 0xff;
-    new_blue -= ColorTransformDelta(m->green_to_blue_, green);
-    new_blue -= ColorTransformDelta(m->red_to_blue_, red);
+    new_blue -= ColorTransformDelta((int8_t)m->green_to_blue_, green);
+    new_blue -= ColorTransformDelta((int8_t)m->red_to_blue_, red);
     new_blue &= 0xff;
     data[i] = (argb & 0xff00ff00u) | (new_red << 16) | (new_blue);
   }
@@ -560,7 +560,7 @@ static WEBP_INLINE uint8_t TransformColorRed(uint8_t green_to_red,
                                              uint32_t argb) {
   const int8_t green = U32ToS8(argb >> 8);
   int new_red = argb >> 16;
-  new_red -= ColorTransformDelta(green_to_red, green);
+  new_red -= ColorTransformDelta((int8_t)green_to_red, green);
   return (new_red & 0xff);
 }
 
@@ -570,8 +570,8 @@ static WEBP_INLINE uint8_t TransformColorBlue(uint8_t green_to_blue,
   const int8_t green = U32ToS8(argb >>  8);
   const int8_t red   = U32ToS8(argb >> 16);
   uint8_t new_blue = argb & 0xff;
-  new_blue -= ColorTransformDelta(green_to_blue, green);
-  new_blue -= ColorTransformDelta(red_to_blue, red);
+  new_blue -= ColorTransformDelta((int8_t)green_to_blue, green);
+  new_blue -= ColorTransformDelta((int8_t)red_to_blue, red);
   return (new_blue & 0xff);
 }