spi: core: Initialize returned status in spi_setup

The previous commit that made bits-per-word validation conditional
results in leaving no unconditional affectation of the status variable.

Since the variable is returned at the end of the function, initialize
it to avoid returning an undefined value.

Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Fixes: b3fe2e51 ("spi: core: Only check bits_per_word validity when explicitly provided")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Link: https://lore.kernel.org/r/20220414084040.975520-1-paul.kocialkowski@bootlin.com


Signed-off-by: Mark Brown <broonie@kernel.org>