Fix dtb variable name

Using $dtb which isn't defined causes the boot.img creation fail
Merge pull request #25 from KINGbabasula/patch-1

Fix dtb variable name
Merge remote-tracking branch 'Tasssadar/master'
mrom: lzma support
Bump version to "28x"

Where "x" stands for "Xperia"
Merge remote-tracking branch 'Tasssadar/master'
Merge remote-tracking branch 'XperiaMultirom/master'