iio.h: fix typo in doc parameter section for one function

Fix doc error pointed out by Doxygen warning/error checking now in CI.
(which actually means the previous commits worked :)

From CI log:

2678/docker_build_dir/iio.h:269: warning: argument 'ctx' of command @param is not found in the argument list of iio_scan_block_destroy(struct iio_scan_block *blk)
2679/docker_build_dir/iio.h:275: warning: The following parameters of iio_scan_block_destroy(struct iio_scan_block *blk) are not documented:

Signed-off-by: Robin Getz <[email protected]>

Author: rgetz

iio.h

@@ -267,7 +267,7 @@ __api struct iio_scan_block * iio_create_scan_block(
 
 
 /** @brief Destroy the given scan block
- * @param ctx A pointer to an iio_scan_block structure
+ * @param blk A pointer to an iio_scan_block structure
  *
  * <b>NOTE:</b> After that function, the iio_scan_block pointer shall be invalid.
  *