highmem: fix a memory copy problem in memcpy_from_folio

Clang static checker complains that value stored to 'from' is never read. 
And memcpy_from_folio() only copy the last chunk memory from folio to
destination.  Use 'to += chunk' to replace 'from += chunk' to fix this
typo problem.

Link: https://lkml.kernel.org/r/[email protected]
Fixes: b23d03e ("highmem: add memcpy_to_folio() and memcpy_from_folio()")
Signed-off-by: Su Hui <[email protected]>
Reviewed-by: Matthew Wilcox (Oracle) <[email protected]>
Cc: Ira Weiny <[email protected]>
Cc: Jiaqi Yan <[email protected]>
Cc: Nathan Chancellor <[email protected]>
Cc: Nick Desaulniers <[email protected]>
Cc: Peter Collingbourne <[email protected]>
Cc: Tom Rix <[email protected]>
Cc: Tony Luck <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: Su Hui

include/linux/highmem.h

@@ -454,7 +454,7 @@ static inline void memcpy_from_folio(char *to, struct folio *folio,
 		memcpy(to, from, chunk);
 		kunmap_local(from);
 
-		from += chunk;
+		to += chunk;
 		offset += chunk;
 		len -= chunk;
 	} while (len > 0);