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/maps/vmu-flash.c b/drivers/mtd/maps/vmu-flash.c
index 3a04b07..48a803e 100644
--- a/drivers/mtd/maps/vmu-flash.c
+++ b/drivers/mtd/maps/vmu-flash.c
@@ -544,9 +544,9 @@
 	mtd_cur->flags = MTD_WRITEABLE|MTD_NO_ERASE;
 	mtd_cur->size = part_cur->numblocks * card->blocklen;
 	mtd_cur->erasesize = card->blocklen;
-	mtd_cur->write = vmu_flash_write;
-	mtd_cur->read = vmu_flash_read;
-	mtd_cur->sync = vmu_flash_sync;
+	mtd_cur->_write = vmu_flash_write;
+	mtd_cur->_read = vmu_flash_read;
+	mtd_cur->_sync = vmu_flash_sync;
 	mtd_cur->writesize = card->blocklen;
 
 	mpart = kmalloc(sizeof(struct mdev_part), GFP_KERNEL);