patches/openwrt: mpc85xx: switch to kernel 5.15

It seems that switch is no longer starting for almost ~5 minutes, but it is
working immediately. So, let's use switch to kernel 5.15 instead of
kernel 5.10.

patches/openwrt/wip/0000-mpc85xx-and-mvebu-switch-to-kernel-5.15.patch

@@ -17,7 +17,7 @@ index b1771dfd8e..35d08b12d1 100644
  SUBTARGETS:=p1010 p1020 p2020
  
 -KERNEL_PATCHVER:=5.4
-+KERNEL_PATCHVER:=5.10
++KERNEL_PATCHVER:=5.15
 +KERNEL_TESTING_PATCHVER:=5.15
  
  KERNELNAME:=zImage