RDMA/ocrdma: Help gcc generate better code for ocrdma_srq_toggle_bit

gcc emits a surprising amount of code in order to flip a bit. One
would think that a single instruction is enough.

$ scripts/bloat-o-meter /tmp/ocrdma_verbs.o drivers/infiniband/hw/ocrdma/ocrdma_verbs.o
add/remove: 0/0 grow/shrink: 0/3 up/down: 0/-142 (-142)
function                                     old     new   delta
ocrdma_post_srq_recv                         498     460     -38
ocrdma_poll_cq                              2010    1962     -48
ocrdma_discard_cqes                          495     439     -56

All three calls of ocrdma_srq_toggle_bit happen within spinlocks, so
saving a few useless instructions might be worthwhile.
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Acked-by: Selvin Xavier <selvin.xavier@emulex.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>

drivers/infiniband/hw/ocrdma/ocrdma_verbs.c

@@ -1591,10 +1591,7 @@ static void ocrdma_srq_toggle_bit(struct ocrdma_srq *srq, int idx)
 	int i = idx / 32;
 	unsigned int mask = (1 << (idx % 32));
 
-	if (srq->idx_bit_fields[i] & mask)
-		srq->idx_bit_fields[i] &= ~mask;
-	else
-		srq->idx_bit_fields[i] |= mask;
+	srq->idx_bit_fields[i] ^= mask;
 }
 
 static int ocrdma_hwq_free_cnt(struct ocrdma_qp_hwq_info *q)