Apply commit 5a821e2d69e2 ("powerpc/boot: Fix build with gcc 15") to stable kernels

[Christophe Leroy]

Hi,

Could you please apply commit 5a821e2d69e2 ("powerpc/boot: Fix build 
with gcc 15") to stable kernels, just like you did with commit 
ee2ab467bddf ("x86/boot: Use '-std=gnu11' to fix build with GCC 15")

Ref: https://bugzilla.kernel.org/show_bug.cgi?id=220407

Thanks
Christophe