IB/ipath: Trivial simplification of ipath_make_ud_req()

Move the increment of s_hdrwords into the existing if block that tests
if we're doing a send with immediate, to save one test of the opcode.

Signed-off-by: Ralph Campbell <ralph.campbell@qlogic.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>