[GFS2] Fix bz 229873, alternate test: assertion "!ip->i_inode.i_mapping->nrpages" failed

The following removes an incorrect assertion from the GFS2 glops code. This
fixes Red Hat bz 229873. Thanks to Abhijith Das for testing the patch
and confirming the fix.

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
Cc: Abhijith Das <adas@redhat.com>