p54: Use do_div for 64-bit division to fix 32-bit kernels

Use the do_div macro for 64-bit division. Otherwise, the module will
reference __udivdi3 under 32-bit kernels, which is not allowed in
kernel space.

Signed-off-by: Christian Lamparter <chunkeey@googlemail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>