PCI: rcar: Poll more often in rcar_pcie_wait_for_dl()

The data link active signal usually takes ~20 uSec to be asserted, poll
the bit more often to avoid useless delays in this function.

Use udelay() instead of usleep() for such a small delay as suggested by
the timer documentation.

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
[lorenzo.pieralisi@arm.com: updated commit log]
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Cc: Geert Uytterhoeven <geert+renesas@glider.be>
Cc: Phil Edworthy <phil.edworthy@renesas.com>
Cc: Simon Horman <horms+renesas@verge.net.au>
Cc: Wolfram Sang <wsa@the-dreams.de>
Cc: linux-renesas-soc@vger.kernel.org