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/FileSystem/FileDescription.cpp

@@ -203,7 +203,7 @@ KResultOr<NonnullOwnPtr<KBuffer>> FileDescription::read_entire_file()
     return m_inode->read_entire(this);
 }
 
-KResultOr<ssize_t> FileDescription::get_dir_entries(UserOrKernelBuffer& output_buffer, ssize_t size)
+KResultOr<size_t> FileDescription::get_dir_entries(UserOrKernelBuffer& output_buffer, size_t size)
 {
     Locker locker(m_lock, Lock::Mode::Shared);
     if (!is_directory())
@@ -213,9 +213,6 @@ KResultOr<ssize_t> FileDescription::get_dir_entries(UserOrKernelBuffer& output_b
     if (!metadata.is_valid())
         return EIO;
 
-    if (size < 0)
-        return EINVAL;
-
     size_t remaining = size;
     KResult error = KSuccess;
     u8 stack_buffer[PAGE_SIZE];