EDAC/sifive: Fix non-kernel-doc comment

scripts/kernel-doc complains about a comment that begins with "/**"
but is not in kernel-doc format, so correct it.

Prevents this warning:

  drivers/edac/sifive_edac.c:23: warning: This comment starts with '/**', \
  but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst
    * EDAC error callback

Fixes: 91abaeaa ("EDAC/sifive: Add EDAC platform driver for SiFive SoCs")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20211201030913.10283-1-rdunlap@infradead.org