rt2800: do not overwrite WPDMA_GLO_CFG_WP_DMA_BURST_SIZE

We already initlized WPDMA_GLO_CFG_WP_DMA_BURST_SIZE to 3 on
rt2800_init_registers() for USB devices. For PCI devices we will use
HW default setting, which is 2, so patch does not change behaviour
on PCI devices.

Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>