Bluetooth: btrtl: Use kvmemdup to simplify the code

Use kvmemdup instead of kvmalloc() + memcpy() to simplify the code.

No functional change intended.

Signed-off-by: Li Zetao <lizetao1@huawei.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>