arm: ls1021a: Remove the inappropriate use of the function 'sprintf'

As the function 'sprintf' does not check buffer boundaries but outputs
to the buffer 'enet' of fixed size (16), this patch removes the function
'sprintf', and uses 'strcpy' instead. It will assign the character
arrays 'enet' and 'phy' the corresponding character strings.

Signed-off-by: Alison Wang <alison.wang@freescale.com>
Reviewed-by: Joe Hershberger <joe.hershberger@ni.com>
Reviewed-by: York Sun <yorksun@freescale.com>