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/sst25l.c b/drivers/mtd/devices/sst25l.c
index 196fd95..a665eba 100644
--- a/drivers/mtd/devices/sst25l.c
+++ b/drivers/mtd/devices/sst25l.c
@@ -403,9 +403,9 @@
 	flash->mtd.erasesize	= flash_info->erase_size;
 	flash->mtd.writesize	= flash_info->page_size;
 	flash->mtd.size		= flash_info->page_size * flash_info->nr_pages;
-	flash->mtd.erase	= sst25l_erase;
-	flash->mtd.read		= sst25l_read;
-	flash->mtd.write 	= sst25l_write;
+	flash->mtd._erase	= sst25l_erase;
+	flash->mtd._read		= sst25l_read;
+	flash->mtd._write 	= sst25l_write;
 
 	dev_info(&spi->dev, "%s (%lld KiB)\n", flash_info->name,
 		 (long long)flash->mtd.size >> 10);