scsi: ch: add include guard to chio.h

Add a header include guard just in case.

Link: https://lore.kernel.org/r/20190728164643.16335-1-yamada.masahiro@socionext.com


Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>