Documentation/core-api: correct reference to SWIOTLB_DYNAMIC

Commit c93f261d ("Documentation/core-api: add swiotlb documentation")
accidentally refers to CONFIG_DYNAMIC_SWIOTLB in one place, while the
config is actually called CONFIG_SWIOTLB_DYNAMIC.

Correct the reference to the intended config option.
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@redhat.com>
Reviewed-by: Petr Tesarik <petr@tesarici.cz>
Signed-off-by: Christoph Hellwig <hch@lst.de>

Documentation/core-api/swiotlb.rst

@@ -192,7 +192,7 @@ alignment larger than PAGE_SIZE.
 
 Dynamic swiotlb
 ---------------
-When CONFIG_DYNAMIC_SWIOTLB is enabled, swiotlb can do on-demand expansion of
+When CONFIG_SWIOTLB_DYNAMIC is enabled, swiotlb can do on-demand expansion of
 the amount of memory available for allocation as bounce buffers. If a bounce
 buffer request fails due to lack of available space, an asynchronous background
 task is kicked off to allocate memory from general system memory and turn it