btrfs: remove constant parameter to memset_extent_buffer and rename it

The only memset we do is to 0, so sink the parameter to the function and
simplify all calls. Rename the function to reflect the behaviour.

Signed-off-by: David Sterba <dsterba@suse.com>
diff --git a/fs/btrfs/tests/extent-io-tests.c b/fs/btrfs/tests/extent-io-tests.c
index caad80b..2c7a0a9 100644
--- a/fs/btrfs/tests/extent-io-tests.c
+++ b/fs/btrfs/tests/extent-io-tests.c
@@ -306,7 +306,7 @@ static int __test_eb_bitmaps(unsigned long *bitmap, struct extent_buffer *eb,
 	int ret;
 
 	memset(bitmap, 0, len);
-	memset_extent_buffer(eb, 0, 0, len);
+	memzero_extent_buffer(eb, 0, len);
 	if (memcmp_extent_buffer(eb, bitmap, 0, len) != 0) {
 		test_msg("Bitmap was not zeroed\n");
 		return -EINVAL;