lib/iomem_copy: fix kerneldoc format style

The newly added file did not quite get the punctuation right:

lib/iomem_copy.c:14: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202410290907.0mDZVYPK-lkp@intel.com/


Signed-off-by: Arnd Bergmann <arnd@arndb.de>