ubi: use correct names in function kernel-doc comments

Fix kernel-doc warnings by using the correct function names in
their kernel-doc notation:

drivers/mtd/ubi/eba.c:72: warning: expecting prototype for next_sqnum(). Prototype was for ubi_next_sqnum() instead
drivers/mtd/ubi/wl.c:176: warning: expecting prototype for wl_tree_destroy(). Prototype was for wl_entry_destroy() instead
drivers/mtd/ubi/misc.c:24: warning: expecting prototype for calc_data_len(). Prototype was for ubi_calc_data_len() instead

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Richard Weinberger <richard@nod.at>
Cc: Miquel Raynal <miquel.raynal@bootlin.com>
Cc: Vignesh Raghavendra <vigneshr@ti.com>
Cc: linux-mtd@lists.infradead.org
Signed-off-by: Richard Weinberger <richard@nod.at>

drivers/mtd/ubi/eba.c

@@ -61,7 +61,7 @@ struct ubi_eba_table {
 };
 
 /**
- * next_sqnum - get next sequence number.
+ * ubi_next_sqnum - get next sequence number.
  * @ubi: UBI device description object
  *
  * This function returns next sequence number to use, which is just the current

drivers/mtd/ubi/misc.c

@@ -10,7 +10,7 @@
 #include "ubi.h"
 
 /**
- * calc_data_len - calculate how much real data is stored in a buffer.
+ * ubi_calc_data_len - calculate how much real data is stored in a buffer.
  * @ubi: UBI device description object
  * @buf: a buffer with the contents of the physical eraseblock
  * @length: the buffer length

drivers/mtd/ubi/wl.c

@@ -165,7 +165,7 @@ static void wl_tree_add(struct ubi_wl_entry *e, struct rb_root *root)
 }
 
 /**
- * wl_tree_destroy - destroy a wear-leveling entry.
+ * wl_entry_destroy - destroy a wear-leveling entry.
  * @ubi: UBI device description object
  * @e: the wear-leveling entry to add
  *