rules.mk: Fix comment typo
rules.mk: Fix comment typo

Signed-off-by: Marti Bolivar <35e491f5b70a779e5455b1f9617e0073292369ca@leaflabs.com>

OpenMusicKontrollers/chimaera_firmware,OpenMusicKontrollers/chimaera_firmware,OpenMusicKontrollers/chimaera_firmware