Update linux-signed/linux-restricted-modules for forward port suffixes

Impact: When forward-porting kernels we add a +NN.NN.N suffix to the package version. We also append +N to the version for respins of linux-signed and linux-restricted-modules, which gets stripped to determine the version of kernel packages to use in the Build-Depends. The regex which strips +N does not do end-of-line matching, and so it ends up stripping part of the forward-port suffix, causing the wrong version to be placed in the Build-Depends.

Fix: Add end-of-line matching to the regex which strips the +N from the version string, ensuring that this pattern is not stripped from elsewhere in the version.

Test Case: Run 'fakeroot debian/rules clean' in a signed/l-r-m tree for a forward-port kernel and inspect debian/control. Without end-of-line matching the +NN part of +NN.NN.N is stripped from the versions in Build-Depends. With end-of-line matching it is not stripped.

Regression Potential: Any problems will result in incorrect versions placed in the Build-Depends. The most likely result is that this is a package version which does not exist, so the packages fail to build due to missing dependencies. It is very unlikely that an incorrect but valid package version in the Build-Depends, but if this did happen the packages could successfully build against the wrong kernel. This would be noticed quickly in testing as modules from linux-modules will fail to load with the packages produced from the linux-signed build.