Replace roundup() with roundup_64() as we calculate min_logblks
with 64-bit divisions.  Hence, call roundup() will cause the
following error while compiling a 32-bit kernel:

fs/built-in.o: In function `xfs_log_calc_minimum_size':
fs/xfs/xfs_log_rlimit.c:140: undefined reference to `__udivdi3'
Reported-by: NFengguang Wu <fengguang.wu@intel.com>
Cc: Dave Chinner <dchinner@redhat.com>
Signed-off-by: NJie Liu <jeff.liu@oracle.com>
Reviewed-by: NDave Chinner <dchinner@redhat.com>
Signed-off-by: NBen Myers <bpm@sgi.com>