net: ethernet: sun: Zero initialize class in default case in niu_add_ethtool_tcam_entry

When building with -Wsometimes-uninitialized, Clang warns:

drivers/net/ethernet/sun/niu.c:7466:5: warning: variable 'class' is used
uninitialized whenever switch default is taken
[-Wsometimes-uninitialized]

The default case can never happen because i can only be 0 to 3
(NIU_L3_PROG_CLS is defined as 4). To make this clear to Clang,
just zero initialize class in the default case (use the macro
CLASS_CODE_UNRECOG to make it clear this shouldn't happen).

Link: https://github.com/ClangBuiltLinux/linux/issues/403
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>