auto-patchelf: don't use grep -q, as it causes Broken pipe (#56958)

This rare sitation was caught when building zoom-us package:
```
automatically fixing dependencies for ELF files
/nix/store/71d65fplq44y9yn2fvkpn2d3hrszracd-auto-patchelf-hook/nix-support/setup-hook: line 213: echo: write error: Broken pipe
/nix/store/71d65fplq44y9yn2fvkpn2d3hrszracd-auto-patchelf-hook/nix-support/setup-hook: line 210: echo: write error: Broken pipe
```

The worst is that derivation continued and resulted into broken package:
https://github.com/NixOS/nixpkgs/pull/55566#issuecomment-470065690

I hope, replacing `grep -q` with `grep` will remove this race condition.