ath25: fix compilation for AR2315 MTD driver

Kernel commit e7bfb3fdbde3 ("mtd: Stop updating erase_info->state
and calling mtd_erase_callback()") removed erase_info->state
updates and calls of mtd_erase_callback().

Drop these erase callback invocations from AR2315 MTD driver as well.

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>

target/linux/ath25/patches-5.4/120-spiflash.patch

@@ -23,7 +23,7 @@
  obj-$(CONFIG_MTD_POWERNV_FLASH)	+= powernv_flash.o
 --- /dev/null
 +++ b/drivers/mtd/devices/ar2315.c
-@@ -0,0 +1,459 @@
+@@ -0,0 +1,456 @@
 +
 +/*
 + * MTD driver for the SPI Flash Memory support on Atheros AR2315
@@ -284,9 +284,6 @@
 +
 +	mutex_unlock(&priv->lock);
 +
-+	instr->state = MTD_ERASE_DONE;
-+	mtd_erase_callback(instr);
-+
 +	return 0;
 +}
 +