[IB] mthca: fix format of FW version

Mellanox has decided that the components of the firmware version are
really meant to be displayed in decimal, e.g. 0x000400070190 is
version 4.7.400.  Change the format we use from "%x.%x.%x" to
"%d.%d.%d" to match this convention.

Signed-off-by: Roland Dreier <rolandd@cisco.com>