uml: fix hppfs build

Make HoneyPot ProcFS depend on CONFIG_PROC_FS so that it will build.
Recommended by Christoph Hellwig.

Addresses https://bugzilla.kernel.org/show_bug.cgi?id=33692

Reported-by: Simon Danner <danner.simon@gmail.com>
Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Cc: Jeff Dike <jdike@addtoit.com>
Cc: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>