gpio: pca953x: variable 'id' was used twice

sparse  rightfully said:

drivers/gpio/gpio-pca953x.c:771:45: warning: symbol 'id' shadows an earlier one
drivers/gpio/gpio-pca953x.c:742:36: originally declared here

So, name them explicitly 'i2c_id' and 'acpi_id' to avoid any confusion.

Signed-off-by: Wolfram Sang <wsa@the-dreams.de>