spi: omap2-mcspi: remove redundant check for error status

The check to see if status is less than zero is actually redundant
as all previous places where it is -ve have already branched to the
exit paths, so it is never less than zero at the check.

Detected by CoverityScan, CID#1357119 ("Logically dead code")

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Mark Brown <broonie@kernel.org>