tool: selftests: fix spelling typo of 'writting'

writting -> writing

Signed-off-by: Wang Qing <wangqing@vivo.com>
Reviewed-by: Mike Rapoport <rppt@linux.ibm.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

tools/testing/selftests/vm/userfaultfd.c

@@ -894,7 +894,7 @@ static int faulting_process(int signal_test)
 				count_verify[nr]);
 	        }
 		/*
-		 * Trigger write protection if there is by writting
+		 * Trigger write protection if there is by writing
 		 * the same value back.
 		 */
 		*area_count(area_dst, nr) = count;
@@ -922,7 +922,7 @@ static int faulting_process(int signal_test)
 				count_verify[nr]); exit(1);
 		}
 		/*
-		 * Trigger write protection if there is by writting
+		 * Trigger write protection if there is by writing
 		 * the same value back.
 		 */
 		*area_count(area_dst, nr) = count;