Fix truncation of comparison value introduced in 848acd67.

Casting the difference of the two off_t values to size_t may truncate
the result. Doing so before the comparison will therefore break it.
Instead cast the size to off_t to get around the signed versus unsigned
integer expression comparison and then cast the result of the comparison
to size_t again. Should fix #9714.

src/system/kernel/device_manager/devfs.cpp

@@ -487,7 +487,7 @@ translate_partition_access(devfs_partition* partition, off_t& offset,
 	ASSERT(offset >= 0);
 	ASSERT(offset < partition->info.size);
 
-	size = min_c(size, (size_t)(partition->info.size - offset));
+	size = (size_t)min_c((off_t)size, partition->info.size - offset);
 	offset += partition->info.offset;
 }