Fix kernel documentation comments to avoid various warnings when compiling
with W=1.

No functional changes.

Link: https://lore.kernel.org/r/20200706123345.451783-1-damien.lemoal@wdc.comSigned-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>