PCI: rcar: Fix position of MSI enable bit

The MSI enable is bit 31, not bit 28.  Set the correct bit to initialize
MSI.

Per Phil, "this is odd as MSI works before and after your patch. Since bit
31 just represents the value of MSICAP0[16].MSIE, I think this may just be
used for endpoints.  However, you are correct that the bit used was wrong."

Signed-off-by: Nobuhiro Iwamatsu <nobuhiro.iwamatsu.yj@renesas.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Phil Edworthy <phil.edworthy@renesas.com>
Acked-by: Simon Horman <horms+renesas@verge.net.au>