uml: fix infinite mconsole loop

This patch takes care of a problem with the stopping code.

The function inside the while condition returns 0 to signify a problem.  A
problem could be for example a bad command or a bad version of the mconsole
client.  A bad command would terminate the stopping loop and resume the
kernel.  This is a problem.

A better solution is to make the loop infinite and don't leave it until we are
explicitly told to.

Signed-off-by: Karol Swietlicki <magotari@gmail.com>
Signed-off-by: Jeff Dike <jdike@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>