staging: gasket: page table: remove dead code in coherent mem alloc

gasket_alloc_coherent_memory() has some unnecessary code related to out
of memory checking that will never hit the condition checked, remove.

Signed-off-by: Todd Poynor <toddpoynor@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>