mtd: add leading underscore to all mtd functions

This patch renames all MTD functions by adding a "_" prefix:

mtd->erase -> mtd->_erase
mtd->read_oob -> mtd->_read_oob
...

The reason is that we are re-working the MTD API and from now on it is
an error to use MTD function pointers directly - we have a corresponding
API call for every pointer. By adding a leading "_" we achieve the following:

1. Make sure we convert every direct pointer users
2. A leading "_" suggests that this interface is internal and it becomes
   less likely that people will use them directly
3. Make sure all the out-of-tree modules stop compiling and the owners
   spot the big API change and amend them.

Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
diff --git a/drivers/mtd/chips/map_ram.c b/drivers/mtd/chips/map_ram.c
index 67640cc..2253070 100644
--- a/drivers/mtd/chips/map_ram.c
+++ b/drivers/mtd/chips/map_ram.c
@@ -64,11 +64,11 @@
 	mtd->name = map->name;
 	mtd->type = MTD_RAM;
 	mtd->size = map->size;
-	mtd->erase = mapram_erase;
-	mtd->get_unmapped_area = mapram_unmapped_area;
-	mtd->read = mapram_read;
-	mtd->write = mapram_write;
-	mtd->sync = mapram_nop;
+	mtd->_erase = mapram_erase;
+	mtd->_get_unmapped_area = mapram_unmapped_area;
+	mtd->_read = mapram_read;
+	mtd->_write = mapram_write;
+	mtd->_sync = mapram_nop;
 	mtd->flags = MTD_CAP_RAM;
 	mtd->writesize = 1;