vhost: Make parameter name match of vhost_get_vq_desc()

The parameter name in the function declaration and definition
should be the same.

drivers/vhost/vhost.h,
int vhost_get_vq_desc(..., unsigned int iov_count,...);

drivers/vhost/vhost.c,
int vhost_get_vq_desc(..., unsigned int iov_size,...)

Signed-off-by: Xianting Tian <xianting.tian@linux.alibaba.com>
Message-Id: <20230621093835.36878-1-xianting.tian@linux.alibaba.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>