timer: Make sure TIMER_FLAG_MASK bits are free in allocated base

Currently we are using two lowest bit of base for internal purpose and
so they both should be zero in the allocated address. The code was
doing the right thing before this patch came in: commit c5f66e99
(timer: Implement TIMER_IRQSAFE)

Tejun probably forgot to update this piece of code which checks if the
lowest 'n' bits are zero or not and so wasn't updated according to the
new flag. Lets use TIMER_FLAG_MASK in the calculations here.

[ tglx: Massaged changelog ]

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Cc: linaro-kernel@lists.linaro.org
Cc: fweisbec@gmail.com
Cc: tj@kernel.org
Cc: peterz@infradead.org
Link: http://lkml.kernel.org/r/9144e10d7e854a0aa8a673332adec356d81a923c.1393576981.git.viresh.kumar@linaro.org


Signed-off-by: Thomas Gleixner <tglx@linutronix.de>