iwlwifi: earlier rx allocation

Value of count is used to decide when to replenish rx buffers. If it is
equal or above 8 we replenish the buffers. Ensure there is no starvation
by initializing count to 8 - thus forcing replenish at first iteration.

This is helpful when rx receives batches of buffers smaller than 8.

Signed-off-by: Mohamed Abbas <mabbas@linux.intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>