package/libhdhomerun: fix header install path

Header files are expected to be installed in usr/include/libhdhomerun/

https://packages.debian.org/sid/i386/libhdhomerun-dev/filelist
https://github.com/tvheadend/tvheadend/blob/master/src/input/mpegts/tvhdhomerun/tvhdhomerun_private.h#L27



This patch will fix a build error with hdhomerun support enabled in
tvheadend.

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>