btrfs-progs: fix shadow symbols

btrfs-progs: fix shadow symbols

This fixes all the instances of warnings that symbols declared in blocks
shadow symbols with the same name in surrounding scopes:

 cmds-device.c:341:22: warning: symbol 'path' shadows an earlier one
 cmds-device.c:285:14: originally declared here

I just renamed or removed the risky shadow symbols instead of pulling
their blocks out into functions.

Signed-off-by: Zach Brown <zab@redhat.com>
Signed-off-by: David Sterba <dsterba@suse.cz>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>