[PATCH 12/16] xfs: use the common helper uuid_is_null()

From: Amir Goldstein Use the common helper uuid_is_null() and remove the xfs specific helper uuid_is_nil(). The common helper does not check for the NULL pointer value as xfs helper did, but xfs code never calls the helper with a pointer that can be NULL. Conform comments

[PATCH 12/16] xfs: use the common helper uuid_is_null()

From: Amir Goldstein Use the common helper uuid_is_null() and remove the xfs specific helper uuid_is_nil(). The common helper does not check for the NULL pointer value as xfs helper did, but xfs code never calls the helper with a pointer that can be NULL. Conform comments and warning strings