mmc: zynq_sdhci: Fix timeout issue

In the workaround added with 'commit b6f44082 ("mmc: zynq_sdhci: Wait
till sd card detect state is stable")' the timeout variable has post
decrement. Whenever timeout happens, this post decrement is making
timeout=0xffffffff, so timeout error print and return statement are
never reached. Fix it by decrementing it inside the while loop.

Signed-off-by: Ashok Reddy Soma <ashok.reddy.soma@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Link: https://lore.kernel.org/r/61fc1160ada0dd622cd29e381a74af7bf3d9a200.1645625609.git.michal.simek@xilinx.com