tsec: fix the return value for tsec_eth_init()

The Ethernet initialization functions are supposed to return the number of
devices initialized, so fix tsec_eth_init() so that they returns the number of
TSECs initialized, instead of just zero.  This is safe because the return value
is currently ignored by all callers, but now they don't have to ignore it.

In general, if an function initializes only one device, then it should return
a negative number if there's an error.  If it initializes more than one device,
then it should never return a negative number.

Signed-off-by: Timur Tabi <timur@freescale.com>
Signed-off-by: Ben Warren <biggerbadderben@gmail.com>