selftests: rtc: Increase test timeout so that all tests run

The timeout setting for the rtc kselftest is currently 90 seconds. This
setting is used by the kselftest runner to stop running a test if it
takes longer than the assigned value.

However, two of the test cases inside rtc set alarms. These alarms are
set to the next beginning of the minute, so each of these test cases may
take up to, in the worst case, 60 seconds.

In order to allow for all test cases in rtc to run, even in the worst
case, when using the kselftest runner, the timeout value should be
increased to at least 120. Set it to 180, so there's some additional
slack.

Correct operation can be tested by running the following command right
after the start of a minute (low second count), and checking that all
test cases run:

	./run_kselftest.sh -c rtc
Signed-off-by: Nícolas F. R. A. Prado <nfraprado@collabora.com>
Acked-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

tools/testing/selftests/rtc/settings

-timeout=90
+timeout=180