sd: sd_ops: fix DISK_IOCTL_CTRL_SYNC return code

SD IOCTL handling for DISK_IOCTL_CTRL_SYNC was falling through to the
default return statement, and returning an error when disk sync
succeeded. Fix this issue by properly breaking in IOCTL handler.

Signed-off-by: Daniel DeGrasse <daniel.degrasse@nxp.com>