Fix the following doc build warning by correcting path.
doc/guides/rel_notes/release_18_05.rst:285:
WARNING: unknown document: ../rawdevs/ifpga_rawdev
Fixes: 473c88f9b391 ("drivers/raw: remove rawdev from directory names")
Signed-off-by: Jerin Jacob <jerinj@marvell.com>
Acked-by: John McNamara <john.mcnamara@intel.com>