mtd: make few symbols static

Make mtd_group and mtd_groups static since they are only used in this
file.

[Amended by Artem Bityutskiy]
Signed-off-by: NH Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NArtem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: NDavid Woodhouse <David.Woodhouse@intel.com>

drivers/mtd/mtdcore.c

@@ -213,11 +213,11 @@ static struct attribute *mtd_attrs[] = {
 	NULL,
 };
 
-struct attribute_group mtd_group = {
+static struct attribute_group mtd_group = {
 	.attrs		= mtd_attrs,
 };
 
-struct attribute_group *mtd_groups[] = {
+static struct attribute_group *mtd_groups[] = {
 	&mtd_group,
 	NULL,
 };