doc: replace @return by Return:

Sphinx expects Return: and not @return to indicate a return value.

find . -name '*.c' -exec \
sed -i 's/^\(\s\)\*\(\s*\)@return\(\s\)/\1*\2Return:\3/' {} \;

find . -name '*.h' -exec \
sed -i 's/^\(\s\)\*\(\s*\)@return\(\s\)/\1*\2Return:\3/' {} \;

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>

include/linux/zstd.h

@@ -1151,7 +1151,7 @@ struct abuf;
  *
  * @in: Input buffer to decompress
  * @out: Output buffer to hold the results (must be large enough)
- * @return size of the decompressed data, or -ve on error
+ * Return: size of the decompressed data, or -ve on error
  */
 int zstd_decompress(struct abuf *in, struct abuf *out);