qla4xxx: Use kmemdup instead of kmalloc + memcpy

This issue was reported by coccicheck using the semantic patch
at scripts/coccinelle/api/memdup.cocci

Signed-off-by: Benoit Taine <benoit.taine@lip6.fr>
Acked-by: Vikas Chaudhary <vikas.chaudhary@qlogic.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>