Driver contains duplicate code. Host interface has numerous request
functions which allocate memory for a request header. Each request
header is different but all contain, as the first member, a hostif_hdr
structure. This structure has size and event members which need to be
set. By defining a helper function to allocate the memory and set the
initial hostif_hdr members code duplication is reduced.

Add function to allocate  memory for a host interface request. Set
'size' and 'event' members. Remove duplicate code using newly defined
function.
Signed-off-by: Tobin C. Harding <me@tobin.cc>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>