[MTD] [NAND] Avoid deadlock in erase callback; release chip lock first.

When the erase callback performs some other action on the flash, it's
highly likely to deadlock unless we actually release the chip lock
before calling it.

Signed-off-by: David Woodhouse <dwmw2@infradead.org>
diff --git a/drivers/mtd/nand/nand_base.c b/drivers/mtd/nand/nand_base.c
index d569121..b4e0e77 100644
--- a/drivers/mtd/nand/nand_base.c
+++ b/drivers/mtd/nand/nand_base.c
@@ -2069,13 +2069,14 @@
  erase_exit:
 
 	ret = instr->state == MTD_ERASE_DONE ? 0 : -EIO;
-	/* Do call back function */
-	if (!ret)
-		mtd_erase_callback(instr);
 
 	/* Deselect and wake up anyone waiting on the device */
 	nand_release_device(mtd);
 
+	/* Do call back function */
+	if (!ret)
+		mtd_erase_callback(instr);
+
 	/*
 	 * If BBT requires refresh and erase was successful, rewrite any
 	 * selected bad block tables