btrfs-progs: check: fix compile warnings in del_file_extent_hole
make[1]: Nothing to be done for `all'.
cmds-check.c: In function ‘del_file_extent_hole’:
cmds-check.c:289:26: warning: ‘prev.start’ may be used uninitialized in this function
cmds-check.c:289:26: warning: ‘prev.len’ may be used uninitialized in this function
cmds-check.c:290:26: warning: ‘next.start’ may be used uninitialized in this function
cmds-check.c:290:26: warning: ‘next.len’ may be used uninitialized in this function
Reported-by: Anand Jain <Anand.Jain@oracle.com>
Signed-off-by: David Sterba <dsterba@suse.cz>