Fix timespec_from_nsec test for 32-bit time_t

Since struct timespec's tv_sec member is of type time_t, adjust the
expected value to allow for the truncation which will occur with 32-bit
time_t.

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Adam Jackson <ajax@redhat.com>
(cherry picked from commit dd1dba80b9)
Closes: https://gitlab.freedesktop.org/mesa/mesa/issues/2043

src/util/tests/timespec/timespec_test.cpp

@@ -206,7 +206,7 @@ TEST(timespec_test, timespec_from_nsec)
 
    timespec_from_nsec(&a, UINT64_MAX);
    EXPECT_EQ(a.tv_nsec, UINT64_MAX % NSEC_PER_SEC);
-   EXPECT_EQ(a.tv_sec, UINT64_MAX / NSEC_PER_SEC);
+   EXPECT_EQ(a.tv_sec, (time_t)(UINT64_MAX / NSEC_PER_SEC));
 }
 
 TEST(timespec_test, timespec_from_usec)