staging: et131x: Avoid unnecessary calculations in for loop

In et131x_rx_dma_memory_alloc(), we loop over fbr_entries - the values of
fbr_align and fbr_chunksize calculated in the loop do not depend on the
loop counter and are the same for all loop iterations.

Take the calculations of these values out of the loop, as we only
need to calculate them once per loop, not once per loop iteration.

Signed-off-by: Mark Einon <mark.einon@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>