rtc: mxc: Silence a clang warning

Change the of_device_get_match_data() cast to (uintptr_t)
to silence the following clang warning:

drivers/rtc/rtc-mxc.c:315:19: warning: cast to smaller integer type 'enum imx_rtc_type' from 'const void *' [-Wvoid-pointer-to-enum-cast]

Reported-by: kernel test robot <lkp@intel.com>
Fixes: ba7aa630

 ("rtc: mxc: use of_device_get_match_data")
Signed-off-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20220526011459.1167197-1-festevam@gmail.com