HSI: omap_ssi_port: Don't print uninitialized err

Do not print err variable, that has nothing to do with the error.
This fixes a warning, that is printed at build time:

drivers/hsi/controllers/omap_ssi_port.c: In function ‘ssi_port_probe’:
drivers/hsi/controllers/omap_ssi_port.c:1121:10: warning: ‘err’ may be used uninitialized in this function [-Wuninitialized]

Signed-off-by: Sebastian Reichel <sre@kernel.org>