MLK-19787 can: flexcan: fix CAN can't receive remote request frame

MLK-19787 can: flexcan: fix CAN can't receive remote request frame

The flexcan driver allocates canfd-skb no matter whether use CAN FD
mode or not, it's unreasonable due to it will affect the parse of the
remote request frame.

To fix the issue, allocating can-skb with "alloc_can_skb()" in normal
mode and canfd-skb with "alloc_canfd_skb()" in fd mode.

Reviewed-by: Dong Aisheng <aisheng.dong@nxp.com>
Signed-off-by: Joakim Zhang <qiangqing.zhang@nxp.com>
Signed-off-by: Arulpandiyan Vadivel <arulpandiyan_vadivel@mentor.com>