Fix some errors in comments

A comment in tests/stringlist.c refers to fdt_get_string(), which is not a
function that exists.  From the content, it's supposed to be referring to
fdt_getprop_string().

A comment in libfdt.h has an extraneous space in a function name.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

libfdt/libfdt.h

@@ -1449,7 +1449,7 @@ int fdt_setprop(void *fdt, int nodeoffset, const char *name,
 		const void *val, int len);
 
 /**
- * fdt_setprop _placeholder - allocate space for a property
+ * fdt_setprop_placeholder - allocate space for a property
  * @fdt: pointer to the device tree blob
  * @nodeoffset: offset of the node whose property to change
  * @name: name of the property to change

tests/stringlist.c

@@ -60,10 +60,11 @@ static void check_expected_failure(const void *fdt, const char *path,
 		FAIL("empty string not found in #address-cells: %d\n", err);
 
 	/*
-	 * fdt_get_string() can successfully extract strings from non-string
-	 * properties. This is because it doesn't necessarily parse the whole
-	 * property value, which would be necessary for it to determine if a
-	 * valid string or string list is present.
+	 * fdt_getprop_string() can successfully extract strings from
+	 * non-string properties. This is because it doesn't
+	 * necessarily parse the whole property value, which would be
+	 * necessary for it to determine if a valid string or string
+	 * list is present.
 	 */
 }