powerpc: Drop unnecessary initializations in __copy_inst_from_kernel_nofault()

Now that the minimum supported version of LLVM for building the kernel
has been bumped to 15.0.0, the zero initializations of val and suffix
added by commit 0d76914a ("powerpc/inst: Optimise
copy_inst_from_kernel_nofault()") to avoid a bogus case of
-Wuninitialized can be dropped because the preprocessor condition is
always false.

Reviewed-by: Kees Cook <kees@kernel.org>
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Link: https://lore.kernel.org/r/20250821-bump-min-llvm-ver-15-v2-6-635f3294e5f0@kernel.org


Signed-off-by: Nathan Chancellor <nathan@kernel.org>