net: wwan: t7xx: check skb_clone in control TX

net: wwan: t7xx: check skb_clone in control TX

t7xx_port_ctrl_tx() clones each skb fragment before passing it to the
port transmit path. The clone is used immediately to set cloned->len, so
an skb_clone() failure results in a NULL pointer dereference.

Check the clone before using it. If previous fragments were already
queued, preserve the driver's existing partial-write behavior by
returning the number of bytes submitted so far.

Fixes: 36bd28c1cb0d ("wwan: core: Support slicing in port TX flow of WWAN subsystem")
Signed-off-by: Ruoyu Wang <ruoyuw560@gmail.com>
Reviewed-by: Loic Poulain <loic.poulain@oss.qualcomm.com>
Link: https://patch.msgid.link/20260612035613.1192486-1-ruoyuw560@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>