IB/srp: Get rid of unneeded use of list_for_each_entry_safe()

list_for_each_entry_safe() is used in one place where the list isn't
modified.  So just change it to list_for_each_entry().

Signed-off-by: Matthew Wilcox <matthew@wil.cx>
Signed-off-by: Roland Dreier <rolandd@cisco.com>