spi: fsl_qspi: Use GENMASK

Replace numeric mask hexcodes with GENMASK macro
in fsl_qspi

Cc: York Sun <yorksun@freescale.com>
Cc: Haikun Wang <Haikun.Wang@freescale.com>
Signed-off-by: NJagan Teki <jteki@openedev.com>

drivers/spi/fsl_qspi.c

@@ -24,7 +24,7 @@ DECLARE_GLOBAL_DATA_PTR;
 #define TX_BUFFER_SIZE		0x40
 #endif
 
-#define OFFSET_BITS_MASK	0x00ffffff
+#define OFFSET_BITS_MASK	GENMASK(24, 0)
 
 #define FLASH_STATUS_WEL	0x02