cputime: Remove irqsave from seqlock readers

The reader side code has no requirement to disable interrupts while
sampling data. The sequence counter is enough to ensure consistency.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>