spi: npcm-fiu: Reuse BITS_PER_BYTE definition

No need to redefine already existing definition.
So, replace custom by generic one.
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20200618170144.57433-1-andriy.shevchenko@linux.intel.comSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-npcm-fiu.c

 // SPDX-License-Identifier: GPL-2.0
 // Copyright (c) 2019 Nuvoton Technology corporation.
 
+#include <linux/bits.h>
 #include <linux/init.h>
 #include <linux/kernel.h>
 #include <linux/device.h>
@@ -177,7 +178,6 @@ enum {
 #define MAP_SIZE_16MB			0x1000000
 #define MAP_SIZE_8MB			0x800000
 
-#define NUM_BITS_IN_BYTE		8
 #define FIU_DRD_MAX_DUMMY_NUMBER	3
 #define NPCM_MAX_CHIP_NUM		4
 #define CHUNK_SIZE			16
@@ -252,8 +252,8 @@ static void npcm_fiu_set_drd(struct npcm_fiu_spi *fiu,
 	fiu->drd_op.addr.buswidth = op->addr.buswidth;
 	regmap_update_bits(fiu->regmap, NPCM_FIU_DRD_CFG,
 			   NPCM_FIU_DRD_CFG_DBW,
-			   ((op->dummy.nbytes * ilog2(op->addr.buswidth))
-			    / NUM_BITS_IN_BYTE) << NPCM_FIU_DRD_DBW_SHIFT);
+			   ((op->dummy.nbytes * ilog2(op->addr.buswidth)) / BITS_PER_BYTE)
+			   << NPCM_FIU_DRD_DBW_SHIFT);
 	fiu->drd_op.dummy.nbytes = op->dummy.nbytes;
 	regmap_update_bits(fiu->regmap, NPCM_FIU_DRD_CFG,
 			   NPCM_FIU_DRD_CFG_RDCMD, op->cmd.opcode);