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/pmc551.c b/drivers/mtd/devices/pmc551.c
index cfccf65..67d22e1 100644
--- a/drivers/mtd/devices/pmc551.c
+++ b/drivers/mtd/devices/pmc551.c
@@ -787,11 +787,11 @@
 
 		mtd->size = msize;
 		mtd->flags = MTD_CAP_RAM;
-		mtd->erase = pmc551_erase;
-		mtd->read = pmc551_read;
-		mtd->write = pmc551_write;
-		mtd->point = pmc551_point;
-		mtd->unpoint = pmc551_unpoint;
+		mtd->_erase = pmc551_erase;
+		mtd->_read = pmc551_read;
+		mtd->_write = pmc551_write;
+		mtd->_point = pmc551_point;
+		mtd->_unpoint = pmc551_unpoint;
 		mtd->type = MTD_RAM;
 		mtd->name = "PMC551 RAM board";
 		mtd->erasesize = 0x10000;