net: stmmac: fix a possible endless loop

Port a fix from 5.4.
It forgot to reduce the value of the variable retry in a while loop
in the ethqos_configure() function. It may cause an endless loop and
without timeout.

Change-Id: Icf3887476de6bee7976eb020d18fc9f733324599
Acked-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Sunil Paidimarri <hisunil@codeaurora.org>