stm32: Fix passing invalid argument to RTC callback.

[yn386]

Summary

The folling code does not work with NUCLEO_F401RE.

from pyb import RTC

def cb(v):
    print(v)

rtc=RTC()
rtc.wakeup(1000, cb)

NameError exception occurred with following message.
The argument of callback should be accessed without exception.

Traceback (most recent call last):
  File "<stdin>", line 2, in cb
NameError: local variable referenced before assignment

To fix this issue, this PR passes EXTI_RTC_WAKEUP to callback argument.
This is equivalent behavior with ExtInt callback when ExtInt is mapped to RTC interrupt by passing an integer value.

Testing

Tested with NUCLEO_F401RE.
The argument of callback can be read (22 with NUCLEO_F401RE).

[github-actions]

Code size report:

  mpy-cross:    +0 +0.000% 
   bare-arm:    +0 +0.000% 
minimal x86:    +0 +0.000% 
   unix x64:    +0 +0.000% standard
      stm32:    +8 +0.002% PYBV10
     mimxrt:    +0 +0.000% TEENSY40
        rp2:    +0 +0.000% RPI_PICO_W
       samd:    +0 +0.000% ADAFRUIT_ITSYBITSY_M4_EXPRESS
  qemu rv32:    +0 +0.000% VIRT_RV32

[dpgeorge]

Thanks for the fix, this looks correct.