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/m25p80.c b/drivers/mtd/devices/m25p80.c
index 230b02e..f83e4d0 100644
--- a/drivers/mtd/devices/m25p80.c
+++ b/drivers/mtd/devices/m25p80.c
@@ -908,14 +908,14 @@
 	flash->mtd.writesize = 1;
 	flash->mtd.flags = MTD_CAP_NORFLASH;
 	flash->mtd.size = info->sector_size * info->n_sectors;
-	flash->mtd.erase = m25p80_erase;
-	flash->mtd.read = m25p80_read;
+	flash->mtd._erase = m25p80_erase;
+	flash->mtd._read = m25p80_read;
 
 	/* sst flash chips use AAI word program */
 	if (JEDEC_MFR(info->jedec_id) == CFI_MFR_SST)
-		flash->mtd.write = sst_write;
+		flash->mtd._write = sst_write;
 	else
-		flash->mtd.write = m25p80_write;
+		flash->mtd._write = m25p80_write;
 
 	/* prefer "small sector" erase if possible */
 	if (info->flags & SECT_4K) {