i2c: st: fix missing struct parameter description

Fix a missing struct parameter description to allow
warning free W=1 compilation.

Signed-off-by: Alain Volmat <avolmat@me.com>
Reviewed-by: Patrice Chotard <patrice.chotard@st.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

drivers/i2c/busses/i2c-st.c

@@ -434,6 +434,7 @@ static void st_i2c_wr_fill_tx_fifo(struct st_i2c_dev *i2c_dev)
 /**
  * st_i2c_rd_fill_tx_fifo() - Fill the Tx FIFO in read mode
  * @i2c_dev: Controller's private data
+ * @max: Maximum amount of data to fill into the Tx FIFO
  *
  * This functions fills the Tx FIFO with fixed pattern when
  * in read mode to trigger clock.