regulator: mcp16502: Use #ifdef CONFIG_PM_SLEEP around mcp16502_suspend/resume_noirq

mcp16502_suspend/resume_noirq is only used by SET_NOIRQ_SYSTEM_SLEEP_PM_OPS
when CONFIG_PM_SLEEP is defined.
So use #ifdef CONFIG_PM_SLEEP instead CONFIG_SUSPEND guard.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Signed-off-by: Mark Brown <broonie@kernel.org>