OMAP2/3: PRCM: fix misc. compiler warnings

- missing return in omap_prcm_get_reset_sources()
- potential use of uninitialized variable in omap_prcm_arch_reset()

Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>
Signed-off-by: Paul Walmsley <paul@pwsan.com>