mei: move mei_hbm_hdr function from hbm.h the hbm.c

mei_hbm_hder helper function is only used in hbm.c
so there is no need to define it in a header file

Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>