dm: part: Drop the get_dev() method

This is now handled by the legacy block driver. The get_dev() method is
no-longer used. Drop it.
Signed-off-by: NSimon Glass <sjg@chromium.org>

include/part.h

@@ -12,7 +12,6 @@
 
 struct block_drvr {
 	char *name;
-	struct blk_desc* (*get_dev)(int dev);
 	int (*select_hwpart)(int dev_num, int hwpart);
 };