powerpc: Fix 'sparse' checking on PPC64le

'sparse' is architecture agnostic and knows nothing about ELF ABI
version.

Just like it gets arch and powerpc type and endian from Makefile,
it also need to get _CALL_ELF from there, otherwise it won't set
PPC64_ELF_ABI_v2 macro for PPC64le and won't check the correct code.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/ac1312f2451aa558bb2a8806b4d0aa2020f0c176.1644928018.git.christophe.leroy@csgroup.eu

arch/powerpc/Makefile

@@ -213,7 +213,7 @@ CHECKFLAGS	+= -m$(BITS) -D__powerpc__ -D__powerpc$(BITS)__
 ifdef CONFIG_CPU_BIG_ENDIAN
 CHECKFLAGS	+= -D__BIG_ENDIAN__
 else
-CHECKFLAGS	+= -D__LITTLE_ENDIAN__
+CHECKFLAGS	+= -D__LITTLE_ENDIAN__ -D_CALL_ELF=2
 endif
 
 ifdef CONFIG_476FPE_ERR46