IB/hfi1: use kvfree() in sdma.c

Use kvfree() instead of open-coding it.

Signed-off-by: Geliang Tang <geliangtang@163.com>
Acked-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>