selftests: Fix spelling mistake "cann't" -> "cannot"

There is a spelling mistake in an error message. Fix it.

Link: https://lkml.kernel.org/r/20210826121217.12885-1-colin.king@canonical.com
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

tools/testing/selftests/vm/mlock-random-test.c

@@ -70,7 +70,7 @@ int get_proc_locked_vm_size(void)
 		}
 	}
 
-	perror("cann't parse VmLck in /proc/self/status\n");
+	perror("cannot parse VmLck in /proc/self/status\n");
 	fclose(f);
 	return -1;
 }