lavc/iff: rgbn: fix decoding on big endian

Fixes #2193.
Signed-off-by: Paul B Mahol <onemda@gmail.com>

libavcodec/iff.c

@@ -488,7 +488,7 @@ static int decode_byterun(uint8_t *dst, int dst_size,
     return buf - buf_start;
 }
 
-#define DECODE_RGBX_COMMON(pixel_size) \
+#define DECODE_RGBX_COMMON(type) \
     if (!length) { \
         length = bytestream2_get_byte(gb); \
         if (!length) { \
@@ -498,7 +498,7 @@ static int decode_byterun(uint8_t *dst, int dst_size,
         } \
     } \
     for (i = 0; i < length; i++) { \
-        *(uint32_t *)(dst + y*linesize + x * pixel_size) = pixel; \
+        *(type *)(dst + y*linesize + x * sizeof(type)) = pixel; \
         x += 1; \
         if (x >= width) { \
             y += 1; \
@@ -521,7 +521,7 @@ static void decode_rgb8(GetByteContext *gb, uint8_t *dst, int width, int height,
     while (bytestream2_get_bytes_left(gb) >= 4) {
         uint32_t pixel = 0xFF000000 | bytestream2_get_be24(gb);
         length = bytestream2_get_byte(gb) & 0x7F;
-        DECODE_RGBX_COMMON(4)
+        DECODE_RGBX_COMMON(uint32_t)
     }
 }
 
@@ -539,7 +539,7 @@ static void decode_rgbn(GetByteContext *gb, uint8_t *dst, int width, int height,
         uint32_t pixel = bytestream2_get_be16u(gb);
         length = pixel & 0x7;
         pixel >>= 4;
-        DECODE_RGBX_COMMON(2)
+        DECODE_RGBX_COMMON(uint16_t)
     }
 }