drivers: hv: fix up const issue with vmbus_chan_bin_attrs

In commit 9bec9445 ("sysfs: constify attribute_group::bin_attrs"),
the bin_attributes are now required to be const.  Due to merge issues,
the original commit could not modify this structure (it came in through
a different branch.)  Fix this up now by setting the variable properly.

Cc: Thomas Weißschuh <linux@weissschuh.net>
Cc: Naman Jain <namjain@linux.microsoft.com>
Fixes: 9bec9445 ("sysfs: constify attribute_group::bin_attrs")
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>