xen/pvcalls: Remove set but not used variable

Fixes gcc '-Wunused-but-set-variable' warning:

drivers/xen/pvcalls-front.c: In function pvcalls_front_sendmsg:
drivers/xen/pvcalls-front.c:543:25: warning: variable bedata set but not used [-Wunused-but-set-variable]
drivers/xen/pvcalls-front.c: In function pvcalls_front_recvmsg:
drivers/xen/pvcalls-front.c:638:25: warning: variable bedata set but not used [-Wunused-but-set-variable]

They are never used since introduction.

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>