spi: fsl_qspi: fix an error of using GENMASK

This commit fixes the change of below commit
"spi: fsl_qspi: Use GENMASK"
(sha1 :bad490a2)

Signed-off-by: Gong Qianyu <Qianyu.Gong@freescale.com>
Reviewed-by: Jagan Teki <jteki@openedev.com>