IB/ipath: Fix time comparison to use time_after_eq()

Raw comparison against jiffies will fail if jiffies wraps, although
since ipath currently only supports 64-bit architectures, this is rather
far-fetched.  Still, it's better to use time_after_eq().

Signed-off-by: Robert P. J. Day <rpjday@crashcourse.ca>
Signed-off-by: Roland Dreier <rolandd@cisco.com>