staging/slicoss: Remove always true if statement

skbtype is assigned once to NORMAL_ETHFRAME and then checked if it is
NORMAL_ETHFRAME -> remove the checks.

This also gets rid of the (false positive) smatch warning:
slicoss.c:2829 slic_xmit_start() error: potential NULL dereference
'hcmd'.

Signed-off-by: Peter Huewe <peterhuewe@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>