AOSP: ext2simg: fix same_file() to check st_dev

AOSP: ext2simg: fix same_file() to check st_dev

File identity is determined by the combination of st_dev and st_ino, not
by st_ino alone.

This fixes a bug where ext2simg would needlessly make a copy of all the
data when the input and output files happened to have the same st_ino.

Fixes: db6f320912cf ("AOSP: android: add the ext2simg tool")
Change-Id: I94e4bf57d9f91b31e5438768805e9f10bec3411d
Signed-off-by: Eric Biggers <ebiggers@google.com>
From AOSP commit: 0749f83a2cf4c134a2403701ab78388500e53f76