drivers: hv: Get rid of some unnecessary code

The current code unnecessarily limits the number of offers we handle.
Get rid of this limitation. As part of this cleanup, also get rid of an
unused define - MAX_MSG_TYPES.

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>