parisc: Drop WARN_ON_ONCE() from flush_cache_vmap

I have observed warning to occassionally trigger.

Signed-off-by: John David Anglin <dave.anglin@bell.net>
Signed-off-by: Helge Deller <deller@gmx.de>
Cc: stable@vger.kernel.org # v5.12+

Author: danglin44

arch/parisc/kernel/cache.c

@@ -841,7 +841,7 @@ void flush_cache_vmap(unsigned long start, unsigned long end)
 	}
 
 	vm = find_vm_area((void *)start);
-	if (WARN_ON_ONCE(!vm)) {
+	if (!vm) {
 		flush_cache_all();
 		return;
 	}