Pinchfire is one of several herbs and spices that were seemingly invented by GRRM for his various "Thrones" books to give it an 'other-worldly' feel.
There's a pretty complete list of all plants mentioned in the "A Song of Ice and Fire" series here.
The more obviously fictional ones include;
- Pinchfire
- Firepods
- Sting-me-not
- Daggerleaf
- Goldenheart
- Sandbeggar
- Sourleaf
- Spiceflower
- Waspwillow
- Prickly Ben &
- Harpy's Gold
As far as what it actually smells like, it's worth noting that before the advent of deodorant (and toilet paper) herbs and spices were used in great quantities to disguise human smells and to freshen clothing. My personal guess is that pinchfire would be in the same league as cloves or myrrh