An ownership stake of the small St. Louis hospital known for helping inspire the horror novel and film “The Exorcist” is up in the air amid the bankruptcy of a national health care chain. In Chapter 11 bankruptcy filings spanning the last two months, the Florida-based Promise Healthcare Group has sought approval to sell its stake in St. Alexius Hospital in St. Louis — one of dozens of subsidiary health care and nursing home facilities across the country that the company encompasses.