ARM: tegra: fix ignored return value of regulator_enable

This fixes:

arch/arm/mach-tegra/board-harmony-pcie.c: In function ‘harmony_pcie_init’:
arch/arm/mach-tegra/board-harmony-pcie.c:65:18: warning: ignoring return
    value of ‘regulator_enable’, declared with attribute
    warn_unused_result [-Wunused-result]

Signed-off-by: Stephen Warren <swarren@nvidia.com>