utime: fix narrowing conversion compiler warning in sleep()

utime: fix narrowing conversion compiler warning in sleep()

Fix compiler warning:
./include/utime.h: In member function 'void utime_t::sleep()':
./include/utime.h:139:50: warning: narrowing conversion of
 '((utime_t*)this)->utime_t::tv.utime_t::<anonymous struct>::tv_sec' from
 '__u32 {aka unsigned int}' to '__time_t {aka long int}' inside { } is
 ill-formed in C++11 [-Wnarrowing]
./include/utime.h:139:50: warning: narrowing conversion of
 '((utime_t*)this)->utime_t::tv.utime_t::<anonymous struct>::tv_nsec' from
 '__u32 {aka unsigned int}' to 'long int' inside { } is
 ill-formed in C++11 [-Wnarrowing]

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>
(cherry picked from commit 014fc6d6c1c68e2e3ad0117d08c4e46e4030d49e)