EDAC: Make dev_attr_sdram_scrub_rate static

The dev_attr_sdram_scrub_rate is not declared in a header or used
anywhere else, so make it static to fix the following warning:

  drivers/edac/edac_mc_sysfs.c:816:1: warning: symbol
  'dev_attr_sdram_scrub_rate' was not declared. Should it be static?
Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
Reviewed-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Cc: linux-edac <linux-edac@vger.kernel.org>
Link: http://lkml.kernel.org/r/1465407356-7357-1-git-send-email-ben.dooks@codethink.co.ukSigned-off-by: Borislav Petkov <bp@suse.de>

drivers/edac/edac_mc_sysfs.c

@@ -831,7 +831,7 @@ static DEVICE_ATTR(ce_count, S_IRUGO, mci_ce_count_show, NULL);
 static DEVICE_ATTR(max_location, S_IRUGO, mci_max_location_show, NULL);
 
 /* memory scrubber attribute file */
-DEVICE_ATTR(sdram_scrub_rate, 0, mci_sdram_scrub_rate_show,
+static DEVICE_ATTR(sdram_scrub_rate, 0, mci_sdram_scrub_rate_show,
 	    mci_sdram_scrub_rate_store); /* umode set later in is_visible */
 
 static struct attribute *mci_attrs[] = {