nand: mxs: fix error handling for mxs_nand_init

Fix error handling for mxs_nand_init.

The original error handling is wrong for err2 and err1.
Should first free desc[x], then free desc.

This patch also correctly handle err3, should use
MXS_DMA_CHANNEL_AHB_APBH_GPMI0 as the check point.

Cc: Stefano Babic <sbabic@denx.de>
CC: Fabio Estevam <Fabio.Estevam@freescale.com>
Cc: Scott Wood <scottwood@freescale.com>
Cc: Marek Vasut <marex@denx.de>
Signed-off-by: Peng Fan <van.freenix@gmail.com>
Reviewed-by: Marek Vasut <marex@denx.de>