gpio: pca953x: add support for pca9555 I2C I/O expander

Add support for pca9555 I2C I/O expander. As the comment suggests this part
is software compatible with the pca9539.

Signed-off-by: Will Newton <[e-mail]>
Cc: "eric miao" <[e-mail]>
Cc: David Brownell <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/gpio/pca953x.c

···
 	{ "pca9537", 4, },
 	{ "pca9538", 8, },
 	{ "pca9539", 16, },
+	{ "pca9555", 16, },
+	{ "pca9557", 8, },
 	/* REVISIT several pca955x parts should work here too */
 	{ }
 };
···
 {
 	struct pca953x_platform_data *pdata;
 	struct pca953x_chip *chip;
-	int ret, i;
+	int ret;
 
 	pdata = client->dev.platform_data;
 	if (pdata == NULL)