lib: Fix spelling

Change-Id: I999987af9cb44906e3c3135c0351a0cd6eb210ff
Signed-off-by: Martin Roth <martin.roth@se-eng.com>
Reviewed-on: http://review.coreboot.org/3756
Reviewed-by: Dave Frodin <dave.frodin@se-eng.com>
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

src/lib/selfboot.c

@@ -361,7 +361,7 @@ static int build_self_segment_list(
 			       (void *)(intptr_t)ntohll(segment->load_addr));
 			*entry =  ntohll(segment->load_addr);
 			/* Per definition, a payload always has the entry point
-			 * as last segment. Thus, we use the occurence of the
+			 * as last segment. Thus, we use the occurrence of the
 			 * entry point as break condition for the loop.
 			 * Can we actually just look at the number of section?
 			 */