media: cxd2880: don't return unitialized values

drivers/media/dvb-frontends/cxd2880/cxd2880_devio_spi.c:59 cxd2880_io_spi_read_reg() error: uninitialized symbol 'ret'.
drivers/media/dvb-frontends/cxd2880/cxd2880_devio_spi.c:111 cxd2880_io_spi_write_reg() error: uninitialized symbol 'ret'.
drivers/media/dvb-frontends/cxd2880/cxd2880_tnrdmd.c:2985 cxd2880_tnrdmd_set_cfg() error: uninitialized symbol 'ret'.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>