openrisc: Remove kernel-doc marker from ioremap comment

Replace the kernel-doc marker (/**) with a regular comment to fix the
warning:

  arch/openrisc/mm/ioremap.c:108: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst
Signed-off-by: Stafford Horne <shorne@gmail.com>

arch/openrisc/mm/ioremap.c

@@ -104,7 +104,7 @@ void iounmap(volatile void __iomem *addr)
 }
 EXPORT_SYMBOL(iounmap);
 
-/**
+/*
  * OK, this one's a bit tricky... ioremap can get called before memory is
  * initialized (early serial console does this) and will want to alloc a page
  * for its mapping.  No userspace pages will ever get allocated before memory