util/cbfstool: Fix typos

Found by: util/lint/checkpatch.pl --types TYPO_SPELLING --fix-inplace
--strict --terse -f util/cbfstool/*.c

Change-Id: I13a27407bf2bad4b9fadcec8cdbd5889068f13cf
Signed-off-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/38633
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: HAOUAS Elyes <ehaouas@noos.fr>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

util/cbfstool/cbfs-mkpayload.c

@@ -115,7 +115,7 @@ int parse_elf_to_payload(const struct buffer *input, struct buffer *output,
 	}
 
 	/* Now, regular headers - we only care about PT_LOAD headers,
-	 * because thats what we're actually going to load
+	 * because that's what we're actually going to load
 	 */
 
 	for (i = 0; i < headers; i++) {