Invalidate dentry cache for nomedia files

While setting a directory as dirty/clean, the directory path is written in the nomedia file. Invalidate the dentry after writing to the nomedia file.

Fix for inconsistent .nomedia file size

BUG: 276849948
Test: manual
Flag: EXEMPT bugfix
Change-Id: Ic139b1908c041349b32ea87f98f626b2f6cc58ca