ASoC: da7218: avoid 64-bit compile warning

When building the da7218 driver on a 64-bit architecture, we get
a harmless warning:

sound/soc/codecs/da7218.c: In function 'da7218_of_get_id':
sound/soc/codecs/da7218.c:2261:10: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]

This changes the code to use uintptr_t to ensure we have an integer
type of the same size as a pointer and won't get a warning on any
architecture.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Fixes: 4d50934a ("ASoC: da7218: Add da7218 codec driver")
Signed-off-by: Mark Brown <broonie@kernel.org>