SSB: Fix handling of ssb_pmu_get_alp_clock()

SSB: Fix handling of ssb_pmu_get_alp_clock()

Dan Carpenter reported missing brackets which resulted in reading a
wrong crystalfreq value. I also noticed that the result of this
function is ignored.

Reported-By: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Signed-off-by: Michael Buesch <m@bues.ch>
Cc: davem@davemloft.net
Cc: netdev@vger.kernel.org
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/10536/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>