sf: Fix to compute proper sector_size

Upto now flash sector_size is assigned from params which isn't
necessarily a sector size from vendor, so based on the SECT_*
flags from flash_params the erase_size will compute and it will
become the sector_size finally.

Bug report (from Bin Meng):
=> sf probe
SF: Detected SST25VF016B with page size 256 Bytes, erase size 4 KiB,
total 2 MiB, mapped at ffe00000

=> sf erase 0 +100
SF: 65536 bytes @ 0x0 Erased: OK

Signed-off-by: Jagannadha Sutradharudu Teki <jagannadh.teki@gmail.com>
Reported-by: Bin Meng <bmeng.cn@gmail.com>
Tested-by: Bin Meng <bmeng.cn@gmail.com>

drivers/mtd/spi/sf_internal.h

@@ -119,7 +119,8 @@ int sst_write_bp(struct spi_flash *flash, u32 offset, size_t len,
  * @name:		Device name ([MANUFLETTER][DEVTYPE][DENSITY][EXTRAINFO])
  * @jedec:		Device jedec ID (0x[1byte_manuf_id][2byte_dev_id])
  * @ext_jedec:		Device ext_jedec ID
- * @sector_size:	Sector size of this device
+ * @sector_size:	Isn't necessarily a sector size from vendor,
+ *			the size listed here is what works with CMD_ERASE_64K
  * @nr_sectors:	No.of sectors on this device
  * @e_rd_cmd:		Enum list for read commands
  * @flags:		Important param, for flash specific behaviour

drivers/mtd/spi/sf_probe.c

@@ -187,6 +187,9 @@ static int spi_flash_validate_params(struct spi_slave *spi, u8 *idcode,
 		flash->erase_size = flash->sector_size;
 	}
 
+	/* Now erase size becomes valid sector size */
+	flash->sector_size = flash->erase_size;
+
 	/* Look for the fastest read cmd */
 	cmd = fls(params->e_rd_cmd & flash->spi->op_mode_rx);
 	if (cmd) {