Use the list_first_entry() macro in ib_srp instead of open-coding the equivalent,
which makes the source code slightly more descriptive.  The list_first_entry()
macro itself was introduced in kernel 2.6.22.
Signed-off-by: NBart Van Assche <bvanassche@acm.org>
Signed-off-by: NDavid Dillow <dillowda@ornl.gov>
Signed-off-by: NRoland Dreier <rolandd@cisco.com>