Fix typo

Ref: DTC commit cc11e522

Signed-off-by: François Revol <revol@free.fr>
diff --git a/include/libfdt.h b/include/libfdt.h
index b153cc3..7403d5a 100644
--- a/include/libfdt.h
+++ b/include/libfdt.h
@@ -582,7 +582,7 @@
  * value of the property named 'name' in the node /aliases.
  *
  * returns:
- *	a pointer to the expansion of the alias named 'name', of it exists
+ *	a pointer to the expansion of the alias named 'name', if it exists
  *	NULL, if the given alias or the /aliases node does not exist
  */
 const char *fdt_get_alias(const void *fdt, const char *name);