mmc: omap_hsmmc: Fix "Unbalanced pm_runtime_enable!" warning

Otherwise we can get following warning when re-loading the omap_hsmmc
driver module when gpio_twl4030 module is not loaded:

omap_hsmmc omap_hsmmc.0: Unbalanced pm_runtime_enable!
omap_hsmmc omap_hsmmc.0: Unable to grab MMC CD IRQ
omap_hsmmc: probe of omap_hsmmc.0 failed with error -22

Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Chris Ball <cjb@laptop.org>