hwclock: fix compiler warnings [-Wmaybe-uninitialized]

hwclock: fix compiler warnings [-Wmaybe-uninitialized]

sys-utils/hwclock-rtc.c: In function 'synchronize_to_clock_tick_rtc':
sys-utils/hwclock.c:169:28: warning: 'now.tv_usec' may be used uninitialized in this function [-Wmaybe-uninitialized]
sys-utils/hwclock-rtc.c:215:24: note: 'now.tv_usec' was declared here
sys-utils/hwclock.c:168:28: warning: 'now.tv_sec' may be used uninitialized in this function [-Wmaybe-uninitialized]
sys-utils/hwclock-rtc.c:215:24: note: 'now.tv_sec' was declared here
sys-utils/hwclock.c:169:28: warning: 'begin.tv_usec' may be used uninitialized in this function [-Wmaybe-uninitialized]
sys-utils/hwclock-rtc.c:215:17: note: 'begin.tv_usec' was declared here
sys-utils/hwclock.c:168:28: warning: 'begin.tv_sec' may be used uninitialized in this function [-Wmaybe-uninitialized]
sys-utils/hwclock-rtc.c:215:17: note: 'begin.tv_sec' was declared here

Signed-off-by: Karel Zak <kzak@redhat.com>