mfd: db8500-prcmu: Remove check for CONFIG_DBX500_PRCMU_DEBUG

A check for CONFIG_DBX500_PRCMU_DEBUG was added in v3.6. But there's no
Kconfig symbol DBX500_PRCMU_DEBUG. So remove this check.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Lee Jones <lee.jones@linaro.org>