bcm27xx: switch to 5.15

I tested it locally and I couldn't find any regressions, so let's give this a
wider test :).

Signed-off-by: Álvaro Fernández Rojas <[email protected]>

target/linux/bcm27xx/Makefile

@@ -11,8 +11,7 @@ BOARDNAME:=Broadcom BCM27xx
 FEATURES:=audio boot-part display ext4 fpu gpio rootfs-part rtc squashfs usb usbgadget
 SUBTARGETS:=bcm2708 bcm2709 bcm2710 bcm2711
 
-KERNEL_PATCHVER=5.10
-KERNEL_TESTING_PATCHVER:=5.15
+KERNEL_PATCHVER:=5.15
 
 define Target/Description
 	Build firmware image for Broadcom BCM27xx SoC devices.