staging: hv: Convert vmbus driver interface function pointer table to constant

Convert vmbus driver interface function pointer table to constant
The vmbus interface functions are assigned to a constant - vmbus_ops.

Because the vmbus interface function pointer table is converted to a
constant variable -- vmbus_ops, the function GetChannelInterface(),
VmbusGetChannelInterface() and pointer GetChannelInterface are no longer
in use. The deprecated function's work is done by the initialization of
the newly added constant variable vmbus_ops.

I created the new constant variable vmbus_ops and removed the deprecated
function pointer GetChannelInterface in one patch.

Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: Hank Janssen <hjanssen@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>