dm snapshot: remove unnecessary NULL checks before vfree() calls

The vfree() function performs input parameter validation.
Thus the NULL pointer test around vfree() calls is not needed.

This issue was detected by using the Coccinelle software.
Signed-off-by: NMarkus Elfring <elfring@users.sourceforge.net>
Signed-off-by: NMike Snitzer <snitzer@redhat.com>

drivers/md/dm-snap-persistent.c

@@ -200,15 +200,10 @@ static int alloc_area(struct pstore *ps)
 
 static void free_area(struct pstore *ps)
 {
-	if (ps->area)
 	vfree(ps->area);
 	ps->area = NULL;
-
-	if (ps->zero_area)
 	vfree(ps->zero_area);
 	ps->zero_area = NULL;
-
-	if (ps->header_area)
 	vfree(ps->header_area);
 	ps->header_area = NULL;
 }
@@ -605,7 +600,6 @@ static void persistent_dtr(struct dm_exception_store *store)
 	free_area(ps);
 
 	/* Allocated in persistent_read_metadata */
-	if (ps->callbacks)
 	vfree(ps->callbacks);
 
 	kfree(ps);