prevent timespec/timeval to ktime_t overflow

Frank v.  Waveren pointed out that on 64bit machines the timespec to
ktime_t conversion might overflow.  This is also true for timeval to
time_t conversions.  This breaks a "sleep inf" on 64bit machines.

While a timespec/timeval with tx.sec = MAX_LONG is valid by specification
the internal representation of ktime_t is based on nanoseconds.  The
conversion of seconds to nanoseconds overflows for seconds values >=
(MAX_LONG / NSEC_PER_SEC).

Check the seconds argument to the conversion and limit it to the maximum
time which can be represented by ktime_t.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Adrian Bunk <bunk@stusta.de>