mtd: block2mtd: page_read() never returns NULL

page_read() never returns NULL, so we can remove the NULL check here.

Signed-off-by: Ryosuke Saito <raitosyo@gmail.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>