android: Fix off-by-one error when joining strings

When concatenating the strings to form a new command line in the
android bootloader flow, the null-terminator was placed one byte after
the end of the allocated string.

Bug: None
Test: booted a rpi3.
Change-Id: I120e09a77bb1c27980e7ce2b5f9b8961424ed0c3

cmd/android_ab_select.c

@@ -35,7 +35,7 @@ static int do_android_ab_select(cmd_tbl_t *cmdtp, int flag, int argc,
 	/* Android standard slot names are 'a', 'b', ... */
 	slot[0] = ANDROID_BOOT_SLOT_NAME(ret);
 	slot[1] = '\0';
-	setenv(argv[1], slot);
+	env_set(argv[1], slot);
 	printf("ANDROID: Booting slot: %s\n", slot);
 	return CMD_RET_SUCCESS;
 }

common/android_bootloader.c

@@ -200,7 +200,8 @@ static char *strjoin(const char **chunks, char separator)
 		*current = separator;
 		current++;
 	}
-	*current = '\0';
+	/* Replace the last separator by a \0. */
+	current[-1] = '\0';
 	return ret;
 }