PCI: rcar: Move the inbound index check

Since the 'idx' variable value is stored across multiple calls to
rcar_pcie_inbound_ranges() function, and the 'idx' value is used to
index registers which are written, subsequent calls might cause
the 'idx' value to be high enough to trigger writes into nonexistent
registers.

Fix this by moving the 'idx' value check to the beginning of the loop.

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Andrew Murray <andrew.murray@arm.com>
Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Cc: Geert Uytterhoeven <geert+renesas@glider.be>
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: Wolfram Sang <wsa@the-dreams.de>
Cc: linux-renesas-soc@vger.kernel.org