variables: add branch to TWRP version number

Since the 9.0 and 10.0 TWRP branches have diverged due to adding
dynamic partition support, this will make it easier to understand
which branch of TWRP is being used for the build.

Change-Id: I2712c9498c9230e9a6d2eac718bda9e82a6d14f7
1 file changed