Kernel: Remove various other uses of ssize_t

Author: https://github.com/gunnarbeutner
Commit: bc3076f894
Pull-request: https://github.com/SerenityOS/serenity/pull/8093
Reviewed-by: https://github.com/awesomekling

Kernel/VM/Region.cpp

@@ -541,7 +541,7 @@ PageFaultResponse Region::handle_inode_fault(size_t page_index_in_region, Scoped
     // Reading the page may block, so release the MM lock temporarily
     mm_lock.unlock();
 
-    KResultOr<ssize_t> result(KSuccess);
+    KResultOr<size_t> result(KSuccess);
     {
         ScopedLockRelease release_paging_lock(vmobject().m_paging_lock);
         auto buffer = UserOrKernelBuffer::for_kernel_buffer(page_buffer);