spi: imx: Fix freeing of DMA channels if spi_bitbang_start() fails

spi: imx: Fix freeing of DMA channels if spi_bitbang_start() fails

If the SPI controller has has_dmamode = true and spi_bitbang_start() fails
in spi_imx_probe(), then the driver must release the DMA channels acquired
in spi_imx_sdma_init() by calling spi_imx_sdma_exit() in the fail path.

Fixes: f62caccd12c1 ("spi: spi-imx: add DMA support")
Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Fabio Estevam <festevam@gmail.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: NXP Linux Team <linux-imx@nxp.com>
Cc: Robin Gong <b38343@freescale.com>
Cc: Shawn Guo <shawnguo@kernel.org>
Link: https://lore.kernel.org/r/20201005132229.513119-1-marex@denx.de
Signed-off-by: Mark Brown <broonie@kernel.org>