rtc: armada38x: Remove unused variable from armada38x_rtc_set_time()

Remove the 'flags' variable in order to fix the following warning:

drivers/rtc/rtc-armada38x.c:91:22: warning: unused variable 'flags' [-Wunused-variable]

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>