Minor fixes to fastboot_driver

- Make RCString() static
- Add clearer error message for 0 length upload error
- Fix regex hex matching for partition-size
- Move ZLP packet checking to SparseWriteCallback()

Test: build fastboot on glinux
Change-Id: I51a040e07b9698a41f64b35a9e2baa8d575527a9
2 files changed