mtd: nand: gpmi: disable the clocks on errors

We should disable the previously enabled GPMI clocks in the error paths.

Also, when gpmi_enable_clk() fails simply return the error
code immediately rather than jumping to to the 'err_out' label.

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Reviewed-by: Marek Vasut <marex@denx.de>
Acked-by: Han Xu <han.xu@nxp.com>
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>