adb: Don't unlink special files on sync failure.

adb push some_disk_image /dev/block/mmcblk0p9
should not unlink the dev just because adb was ctrl-c'd.

Change-Id: I1b6669e8dba1f80fc1438b8deb618180b7e9a1b2
Signed-off-by: JP Abgrall <jpa@google.com>