Check the return value of clk_prepare_enable to ensure that priv->clk has
been successfully enabled.
If priv->clk was not enabled during bcm_sysport_probe, bcm_sysport_resume,
or bcm_sysport_open, it must not be disabled in any subsequent execution
paths.
Found by Linux Verification Center (linuxtesting.org) with Klever.
Fixes: 31bc72d97656 ("net: systemport: fetch and use clock resources")
Signed-off-by: Vitalii Mordan <mordan@xxxxxxxxx>