ext2: Remove GFP_NOFS use in ext2_xattr_cache_insert()

ext2_xattr_cache_insert() calls mb_cache_entry_create() with GFP_NOFS
because it is called under EXT2_I(inode)->xattr_sem. However xattr_sem
or any higher ranking lock is not acquired on fs reclaim path for ext2
at least since we don't do page writeback from direct reclaim.  Thus
GFP_NOFS is not needed.

Signed-off-by: Jan Kara <jack@suse.cz>