memstick: rtsx_usb_ms: Use ms_dev() helper

memstick: rtsx_usb_ms: Use ms_dev() helper

BugLink: https://bugs.launchpad.net/bugs/1811337
Use ms_dev() helper for consistency.

Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
Tested-by: Oleksandr Natalenko <oleksandr@natalenko.name>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
(cherry picked from commit ba9d5f83735fc00297e39ba5cd9ece1c61eb3995)
Signed-off-by: AceLan Kao <acelan.kao@canonical.com>
Acked-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>