fix typos in comments and doc

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

docs/style-guide.txt

@@ -422,7 +422,7 @@ called 'strings.c' - instead of two, food for thought).
 Testing String Equivalence
 ~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-There's a right way and a wrong way to test for sting equivalence with
+There's a right way and a wrong way to test for string equivalence with
 strcmp():
 
 	The wrong way:

scripts/kconfig/util.c

@@ -57,7 +57,7 @@ int file_write_dep(const char *name)
 }
 
 
-/* Allocate initial growable sting */
+/* Allocate initial growable string */
 struct gstr str_new(void)
 {
 	struct gstr gs;