NTB: epf: don't misuse kernel-doc marker

Use "/*" instead of "/**" for common C comments to prevent warnings
from scripts/kernel-doc.

ntb_hw_epf.c:15: warning: expecting prototype for Host side endpoint driver to implement Non(). Prototype was for NTB_EPF_COMMAND() instead

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Jon Mason <jdmason@kudzu.us>
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: Allen Hubbe <allenbh@gmail.com>
Cc: ntb@lists.linux.dev
Signed-off-by: Jon Mason <jdmason@kudzu.us>