ath79: add missing v5.4 SPI chipselect patch

The patch was not applied to the v5.4 target, thus breaking Kernel 5.4
on devices with multiple flash chips attache to the SPI bus.

Fixes commit bd54e73954 ("ath79: set number of chipselect lines")

Signed-off-by: David Bauer <mail@david-bauer.net>

target/linux/ath79/patches-5.4/412-spi-ath79-set-number-of-chipselect-lines.patch

@@ -0,0 +1,26 @@
+From e2e9f6d9f9bd7449ff113c157b639ce1a24b9d3f Mon Sep 17 00:00:00 2001
+From: David Bauer <mail@david-bauer.net>
+Date: Sat, 24 Apr 2021 16:14:48 +0200
+Subject: [PATCH 2/2] spi: ath79: set number of chipselect lines
+
+All chipsets from AR7100 up to QCA9563 have three dedicated chipselect
+lines for the integrated SPI controller. Remove the number of
+chipselects from the platform data, as there is no need to manually set
+this to a different value.
+
+Signed-off-by: David Bauer <mail@david-bauer.net>
+---
+ drivers/spi/spi-ath79.c                 | 2 +-
+ include/linux/platform_data/spi-ath79.h | 1 -
+ 2 files changed, 1 insertion(+), 2 deletions(-)
+
+--- a/drivers/spi/spi-ath79.c
++++ b/drivers/spi/spi-ath79.c
+@@ -187,6 +187,7 @@ static int ath79_spi_probe(struct platfo
+ 	master->use_gpio_descriptors = true;
+ 	master->bits_per_word_mask = SPI_BPW_RANGE_MASK(1, 32);
+ 	master->flags = SPI_MASTER_GPIO_SS;
++	master->num_chipselect = 3;
+ 
+ 	sp->bitbang.master = master;
+ 	sp->bitbang.chipselect = ath79_spi_chipselect;