firmware: xilinx: Add a blank line after function declaration

Fix all these issues which are also reported by checkpatch --strict.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Link: https://lore.kernel.org/r/7b6007e05f6c01214861a37f198cd5bee62a4d3e.1606894725.git.michal.simek@xilinx.com