Staging: hv: Use only one txf buffer per channel and kmalloc/GFP_KERNEL on initialize

Correct issue with not checking kmalloc return value.
This fix now only uses one receive buffer for all hv_utils
channels, and will do only one kmalloc on init and will return
with a -ENOMEM if kmalloc fails on initialize.

And properly clean up memory on failure.

Thanks to Evgeniy Polyakov <zbr@ioremap.net> for pointing this out.
And thanks to Jesper Juhl <jj@chaosbits.net> and Ky Srinivasan
<ksrinivasan@novell.com> for suggesting a better implementation of
my original patch.

Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: Hank Janssen <hjanssen@microsoft.com>
Reviewed-by: Jesper Juhl <jj@chaosbits.net>
Cc: Evgeniy Polyakov <zbr@ioremap.net>
Cc: Jesper Juhl <jj@chaosbits.net>
Cc: Ky Srinivasan <ksrinivasan@novell.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>