m68k: avoid -Wunused-but-set-parameter in clear_user_page()

The loop in clear_user_pages() iterates over all pages and calls
clear_user_page() for each of them.  During the loop "vaddr" is modified. 
However on m68k clear_user() is a macro which does not use "vaddr".  The
compiler sees a variable which is modified but never used and emits a
warning for that:

include/linux/highmem.h: In function 'clear_user_pages':
include/linux/highmem.h:234:63: warning: parameter 'vaddr' set but not used [-Wunused-but-set-parameter=]
    static inline void clear_user_pages(void *addr, unsigned long vaddr,

Other architectures use an inline function for clear_user_page() which
avoids the warning.  This is not possible on m68k, as dlush_dcache_page()
is another macro which is not yet defined where clear_user_page() is
defined.  Including cacheflush_mm.h will trigger recursive and lots of
other issues.

So hide the warning with a cast to (void) instead.

While we are here, do the same for copy_user_page().

Link: https://lore.kernel.org/20260525-m68k-clear_user_page-v2-1-0c8981c6eca1@weissschuh.net
Fixes: 62a9f5a85b ("mm: introduce clear_pages() and clear_user_pages()")
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Andreas Schwab <schwab@linux-m68k.org>
Cc: Ankur Arora <ankur.a.arora@oracle.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

arch/m68k/include/asm/page_mm.h

@@ -55,10 +55,12 @@ static inline void clear_page(void *page)
 #define clear_user_page(addr, vaddr, page)	\
 	do {	clear_page(addr);		\
 		flush_dcache_page(page);	\
+		(void)(vaddr);			\
 	} while (0)
 #define copy_user_page(to, from, vaddr, page)	\
 	do {	copy_page(to, from);		\
 		flush_dcache_page(page);	\
+		(void)(vaddr);			\
 	} while (0)
 
 extern unsigned long m68k_memoffset;