Input: yealink - define packet offset __be16 instead of u16

sparse says

 warning: incorrect type in assignment (different base types)
    expected unsigned short [unsigned] [usertype] offset
    got restricted __be16 [usertype] <noident>

for every usage of cpu_to_be16 in yealink.c. Defining it __be16 in the
first place shouldn't hurt.

Signed-off-by: Martin Kepplinger <martin.kepplinger@ginzinger.com>
Signed-off-by:  <Henk.Vergonet@gmail.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>