epic100: fix use after free on rmmod

epic_close() calls epic_rx() and uses dma buffer, but in epic_remove_one()
we already freed the dma buffer. To fix this issue, reorder function calls
like in the .probe function.

BUG: KASAN: use-after-free in epic_rx+0xa6/0x7e0 [epic100]
Call Trace:
 epic_rx+0xa6/0x7e0 [epic100]
 epic_close+0xec/0x2f0 [epic100]
 unregister_netdev+0x18/0x20
 epic_remove_one+0xaa/0xf0 [epic100]

Fixes: 1da177e4

 ("Linux-2.6.12-rc2")
Reported-by: Yilun Wu <yiluwu@cs.stonybrook.edu>
Signed-off-by: Tong Zhang <ztong0001@gmail.com>
Reviewed-by: Francois Romieu <romieu@fr.zoreil.com>
Link: https://lore.kernel.org/r/20220627043351.25615-1-ztong0001@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>