memstick/ms_block: Use the bitmap API when applicable

Use bitmap_equal() instead of hand writing it. It improves semantic and
avoids some explicit computation to convert a number of bits to a number of
bytes.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/b216df8798f765ab14bce65739c220643320f376.1656155715.git.christophe.jaillet@wanadoo.fr


Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>