powerpc: Avoid comparison of unsigned long >= 0 in __access_ok()

Rewrite function-like macro into regular static inline function to
avoid a warning during macro expansion.

Fix warning (treated as error in W=1):
./arch/powerpc/include/asm/uaccess.h:52:35: error: comparison of unsigned expression >= 0 is always true
   (((size) == 0) || (((size) - 1) <= ((segment).seg - (addr)))))
                                   ^

Suggested-by: Segher Boessenkool <segher@kernel.crashing.org>
Signed-off-by: Mathieu Malaterre <malat@debian.org>
Reviewed-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/uaccess.h

@@ -47,9 +47,13 @@
 
 #else
 
-#define __access_ok(addr, size, segment)	\
-	(((addr) <= (segment).seg) &&		\
-	 (((size) == 0) || (((size) - 1) <= ((segment).seg - (addr)))))
+static inline int __access_ok(unsigned long addr, unsigned long size,
+			mm_segment_t seg)
+{
+	if (addr > seg.seg)
+		return 0;
+	return (size == 0 || size - 1 <= seg.seg - addr);
+}
 
 #endif