mtd: spi-nor: cadence-quadspi: Return error code in cqspi_direct_read_execute()

We return 0 unconditionally in 'cqspi_direct_read_execute()'.
However, 'ret' is set to some error codes in several error handling
paths.

Return 'ret' instead to propagate the error code.

Fixes: ffa639e0

 ("mtd: spi-nor: cadence-quadspi: Add DMA support for direct mode reads")
Cc: <stable@vger.kernel.org>
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>