Update r_rtc.c

[cv007]

Modified the R_RTC_CalendarTimeGet function to allow the time to be read in any code regardless of interrupt state, calculate and populate the time struct tm_yday member, and set the tm_isdst member to the undefined value of -1.

[CLAassistant]

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[renesas-abigail]

This PR is tracked internally by FSPRA-3859.