powerpc: Provide do_ppc64_personality helper

Avoid duplication in future patch that will define the ppc64_personality
syscall handler in terms of the SYSCALL_DEFINE and COMPAT_SYSCALL_DEFINE
macros, by extracting the common body of ppc64_personality into a helper
function.

Signed-off-by: Rohan McLure <rmclure@linux.ibm.com>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220921065605.1051927-15-rmclure@linux.ibm.com

arch/powerpc/kernel/syscalls.c

@@ -74,7 +74,7 @@ SYSCALL_DEFINE6(mmap, unsigned long, addr, size_t, len,
 }
 
 #ifdef CONFIG_PPC64
-long ppc64_personality(unsigned long personality)
+static long do_ppc64_personality(unsigned long personality)
 {
 	long ret;
 
@@ -86,6 +86,10 @@ long ppc64_personality(unsigned long personality)
 		ret = (ret & ~PER_MASK) | PER_LINUX;
 	return ret;
 }
+long ppc64_personality(unsigned long personality)
+{
+	return do_ppc64_personality(personality);
+}
 #endif
 
 long ppc_fadvise64_64(int fd, int advice, u32 offset_high, u32 offset_low,