spidev: fix hang when transfer_one_message fails

This corrects a problem in spi_pump_messages() that leads to an spi
message hanging forever when a call to transfer_one_message() fails.
This failure occurs in my MCP2210 driver when the cs_change bit is set
on the last transfer in a message, an operation which the hardware does
not support.

Rationale
Since the transfer_one_message() returns an int, we must presume that it
may fail.  If transfer_one_message() should never fail, it should return
void.  Thus, calls to transfer_one_message() should properly manage a
failure.

Fixes: ffbbdd21

 (spi: create a message queueing infrastructure)
Signed-off-by: Daniel Santos <daniel.santos@pobox.com>
Signed-off-by: Mark Brown <broonie@linaro.org>
Cc: stable@vger.kernel.org