i2c: piix4: Replace hardcoded memory map size with a #define

i2c: piix4: Replace hardcoded memory map size with a #define

commit 93102cb449780f7b4eecf713451627b78373ce49 upstream.

Replace number constant with #define to improve readability and
maintainability.

Signed-off-by: Terry Bowman <terry.bowman@amd.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Reviewed-by: Jean Delvare <jdelvare@suse.de>
Signed-off-by: Wolfram Sang <wsa@kernel.org>
Cc: Mario Limonciello <Mario.Limonciello@amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>