doxygen: fix some function prototype description

Change-Id: I49311a643ea73143839d2f6bde976cfd76f8c67f
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/6830
Tested-by: jenkins

src/jtag/jtag.h

@@ -546,7 +546,8 @@ int jtag_srst_asserted(int *srst_asserted);
  * @param field Pointer to scan field.
  * @param value Pointer to scan value.
  * @param mask Pointer to scan mask; may be NULL.
- * @returns Nothing, but calls jtag_set_error() on any error.
+ *
+ * returns Nothing, but calls jtag_set_error() on any error.
  */
 void jtag_check_value_mask(struct scan_field *field, uint8_t *value, uint8_t *mask);