sf: Use spi_flash_alloc() in each SPI flash driver

Rather than each device having its own way to allocate a SPI flash
structure, use the new allocation function everywhere. This will make it
easier to extend the interface without breaking devices.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/mtd/spi/macronix.c b/drivers/mtd/spi/macronix.c
index c97a39d..036c30d 100644
--- a/drivers/mtd/spi/macronix.c
+++ b/drivers/mtd/spi/macronix.c
@@ -97,18 +97,12 @@
 		return NULL;
 	}
 
-	flash = malloc(sizeof(*flash));
+	flash = spi_flash_alloc_base(spi, params->name);
 	if (!flash) {
 		debug("SF: Failed to allocate memory\n");
 		return NULL;
 	}
 
-	flash->spi = spi;
-	flash->name = params->name;
-
-	flash->write = spi_flash_cmd_write_multi;
-	flash->erase = spi_flash_cmd_erase;
-	flash->read = spi_flash_cmd_read_fast;
 	flash->page_size = 256;
 	flash->sector_size = 256 * 16 * 16;
 	flash->size = flash->sector_size * params->nr_blocks;