IB/qib: Add missing serdes init sequence

Research has shown that commit a77fcf895046 ("IB/qib: Use a single
txselect module parameter for serdes tuning") missed a key serdes init
sequence.

This patch add that sequence.

Cc: <stable@vger.kernel.org>
Reviewed-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>

drivers/infiniband/hw/qib/qib_iba7322.c

@@ -2395,6 +2395,11 @@ static int qib_7322_bringup_serdes(struct qib_pportdata *ppd)
 	qib_write_kreg_port(ppd, krp_ibcctrl_a, ppd->cpspec->ibcctrl_a);
 	qib_write_kreg(dd, kr_scratch, 0ULL);
 
+	/* ensure previous Tx parameters are not still forced */
+	qib_write_kreg_port(ppd, krp_tx_deemph_override,
+		SYM_MASK(IBSD_TX_DEEMPHASIS_OVERRIDE_0,
+		reset_tx_deemphasis_override));
+
 	if (qib_compat_ddr_negotiate) {
 		ppd->cpspec->ibdeltainprog = 1;
 		ppd->cpspec->ibsymsnap = read_7322_creg32_port(ppd,