docs: printk-formats: fix build warning

Add an empty line after the '::' starting the code block so that the
following lines are properly interpreted.

Without this, the following build warnings are visible.

Documentation/core-api/printk-formats.rst:136: WARNING: Unexpected indentation.
Documentation/core-api/printk-formats.rst:137: WARNING: Block quote ends without a blank line; unexpected unindent.

Fixes: 9294523e3768 ("module: add printk formats to add module build ID to stacktraces")
Signed-off-by: Ioana Ciornei <[email protected]>
Reviewed-by: Stephen Boyd <[email protected]>
Acked-by: Petr Mladek <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jonathan Corbet <[email protected]>

0 files changed, 0 insertions, 0 deletions