greybus: svc: fix endianness for svc message

Some fields in svc request were not being set with the correct
endianness, which will trigger the following sparse issues as example:

greybus/svc.c:116:22: warning: incorrect type in assignment (different base types)
greybus/svc.c:116:22:    expected unsigned short [unsigned] [assigned] [usertype] attr
greybus/svc.c:116:22:    got restricted __le16 [usertype] <noident>

Signed-off-by: Rui Miguel Silva <rui.silva@linaro.org>
Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>