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/devices/block2mtd.c b/drivers/mtd/devices/block2mtd.c
index e7e46d1..d9e75da 100644
--- a/drivers/mtd/devices/block2mtd.c
+++ b/drivers/mtd/devices/block2mtd.c
@@ -285,11 +285,11 @@
 	dev->mtd.writesize = 1;
 	dev->mtd.type = MTD_RAM;
 	dev->mtd.flags = MTD_CAP_RAM;
-	dev->mtd.erase = block2mtd_erase;
-	dev->mtd.write = block2mtd_write;
-	dev->mtd.writev = mtd_writev;
-	dev->mtd.sync = block2mtd_sync;
-	dev->mtd.read = block2mtd_read;
+	dev->mtd._erase = block2mtd_erase;
+	dev->mtd._write = block2mtd_write;
+	dev->mtd._writev = mtd_writev;
+	dev->mtd._sync = block2mtd_sync;
+	dev->mtd._read = block2mtd_read;
 	dev->mtd.priv = dev;
 	dev->mtd.owner = THIS_MODULE;