staging: hv: update dist release parsing in hv_kvp_daemon

The current code to parse the distribution file handles only files with
at least 3 lines. openSuSE has 2 lines and Redhat only one (according to
google).
Update the parser to handle up to three lines properly. Also make the
buffer allocation dynamic and remove a few casts to avoid compiler
warnings.

Signed-off-by: Olaf Hering <olaf@aepfle.de>
Acked-by: KY Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>