xen/blkfront: fix data size for xenbus_gather in connect()

xen/blkfront: fix data size for xenbus_gather in connect()

From: Marek Marczykowski <marmarek@mimuw.edu.pl>

barrier variable is int, not long. This overflow caused another
variable override: "err" (in PV code) and "binfo" (in xenlinux code -
drivers/xen/blkfront/blkfront.c). The latter caused incorrect device
flags (RO/removable etc).

Signed-off-by: Marek Marczykowski <marmarek@mimuw.edu.pl>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Signed-off-by: Jan Beulich <jbeulich@novell.com>