cxl: Fix wrong comparison in cxl_adapter_context_get()

Function atomic_inc_unless_negative() returns a bool to indicate
success/failure. However cxl_adapter_context_get() wrongly compares
the return value against '>=0' which will always be true. The patch
fixes this comparison to '==0' there by also fixing this compile time
warning:

drivers/misc/cxl/main.c:290 cxl_adapter_context_get()
warn: 'atomic_inc_unless_negative(&adapter->contexts_num)' is unsigned

Fixes: 70b565bbdb91 ("cxl: Prevent adapter reset if an active context exists")
Cc: [e-mail] # v4.9+
Reported-by: Dan Carpenter <[e-mail]>
Signed-off-by: Vaibhav Jain <[e-mail]>
Acked-by: Andrew Donnellan <[e-mail]>
Acked-by: Frederic Barrat <[e-mail]>
Signed-off-by: Michael Ellerman <[e-mail]>

drivers/misc/cxl/main.c

···
 	int rc;
 
 	rc = atomic_inc_unless_negative(&adapter->contexts_num);
-	return rc >= 0 ? 0 : -EBUSY;
+	return rc ? 0 : -EBUSY;
 }
 
 void cxl_adapter_context_put(struct cxl *adapter)