mm/hmm.c: remove unused variables align_start and align_end

Variables align_start and align_end are being assigned but are never
used hence they are redundant and can be removed.

Cleans up clang warnings:
  warning: variable 'align_start' set but not used [-Wunused-but-set-variable]
  warning: variable 'align_size' set but not used [-Wunused-but-set-variable]

Link: http://lkml.kernel.org/r/20180714161124.3923-1-colin.king@canonical.com
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/hmm.c

@@ -973,10 +973,7 @@ static RADIX_TREE(hmm_devmem_radix, GFP_KERNEL);
 
 static void hmm_devmem_radix_release(struct resource *resource)
 {
-	resource_size_t key, align_start, align_size;
-
-	align_start = resource->start & ~(PA_SECTION_SIZE - 1);
-	align_size = ALIGN(resource_size(resource), PA_SECTION_SIZE);
+	resource_size_t key;
 
 	mutex_lock(&hmm_devmem_lock);
 	for (key = resource->start;