drivers/misc/vmw_balloon.c: determine page allocation flag can_sleep outside loop

In vmballoon_reserve_page(), flags has been passed from the callee
function (vmballoon_inflate here).  So, we can determine can_sleep outside
the loop.

Signed-off-by: Rakib Mullick <rakib.mullick@gmail.com>
Acked-by: Dmitry Torokhov <dtor@vmware.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>