scarthgap: poco_1.12.5p2: unable to build

[chirag-jn]

The SRC_URI is specified as:
git://github.com/pocoproject/poco.git;branch=master;protocol=https
However, the master branch is not available anymore in poco.git, hence it has to replaced with some other branch.
Upon close inspection, it was observed that SRCREV 1d6fb3e1383e559cacbada5e3f861c0dafaf5d30 is available on the branch poco-1.12.5 in poco.git.
Hence, changing branch name should be sufficient.