test/stm32f_rtc: Allow running the test multiple times
test/stm32f_rtc: Allow running the test multiple times

This allows running the test back-to-back at the console during
a single boot.

BRANCH=none
BUG=b:194720920
TEST=./test/run_device_tests.py --board bloonchipper --tests stm32f_rtc
     minicom -D$(dut-control -o raw_fpmcu_console_uart_pty)
     > runtest
     > runtest

Change-Id: Ibe986d0482bc3dd9a07a7cc0a4f6bf55c5d4c466
Signed-off-by: Craig Hesling <383db090fd8ef907a606ac8a9eccd2962bc489cf@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/3055120
Reviewed-by: Patryk Duda <213d388d1c6ea6afd34b87da9fc4415c3231b04c@google.com>
Reviewed-by: Jack Rosenthal <d3f605bef1867f59845d4ce6e4f83b8dc9e4e0ae@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec