Makefile: Fix typo in `make help` output

Change-Id: I124e7d68198050616795a67df23b6481f6fe1276
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/77407
Reviewed-by: Elyes Haouas <ehaouas@noos.fr>
Reviewed-by: Felix Singer <service+coreboot-gerrit@felixsinger.de>
Reviewed-by: Paul Menzel <paulepanter@mailbox.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

Makefile

@@ -85,7 +85,7 @@ help_coreboot help::
 	@echo  '  clean                 - Remove coreboot build artifacts'
 	@echo  '  distclean             - Remove build artifacts and config files'
 	@echo  '  sphinx                - Build sphinx documentation for coreboot'
-	@echo  '  sphinx-lint           - Build sphinx documenttion for coreboot with warnings as errors'
+	@echo  '  sphinx-lint           - Build sphinx documentation for coreboot with warnings as errors'
 	@echo  '  filelist              - Show files used in current build'
 	@echo  '  printall              - print makefile info for debugging'
 	@echo  '  gitconfig             - set up git to submit patches to coreboot'