spi: imx: Fix failure path leak on GPIO request error correctly

In commit 974488e4 ("spi: imx: Fix failure path leak on GPIO request
error"), spi_bitbang_start() was moved later in the probe sequence.  But
this doesn't work, as spi_bitbang_start() has to be called before
requesting GPIOs because the GPIO data in the spi master is populated when
the master is registed, and that doesn't happen until spi_bitbang_start()
is called.  The default only works if one uses one CS.

So add a failure path call to spi_bitbang_stop() to fix the leak.

CC: Shawn Guo <shawnguo@kernel.org>
CC: Sascha Hauer <kernel@pengutronix.de>
CC: Fabio Estevam <fabio.estevam@nxp.com>
CC: Mark Brown <broonie@kernel.org>
CC: Oleksij Rempel <o.rempel@pengutronix.de>
Signed-off-by: Trent Piepho <tpiepho@impinj.com>
Reviewed-by: Oleksij Rempel <o.rempel@pengutronix.de>
Signed-off-by: Mark Brown <broonie@kernel.org>