community/tlp: Add missing dependency on GNU grep

Upstream is only testing their code against GNU grep, including using ERE expressions that are not POSIX conformat and fail with busybox grep. Upstream made clear in linrunner/TLP#475 that busybox is not supported, so i didn't patch the regexes against upstreams decisions.

Bogus ERE: RE_ATA_ERROR in func.d/tlp-func-stat