Fix copy offset when uploading initial mip data in Vulkan

This is a fix to an original fix which was reverted

BUG=skia:

Change-Id: I21fcda28a5d342984784a35d2b3e985c6e4199cf
Reviewed-on: https://skia-review.googlesource.com/10290
Commit-Queue: Greg Daniel <egdaniel@google.com>
Reviewed-by: Jim Van Verth <jvanverth@google.com>
1 file changed