soc: qcom: service-locator: update types in get_service_location()

Currently, get_service_location() expects "char *" for client
name and service name from clients. Update this to "const char *"
as they're not supposed to be changed by service locator. This
also helps clients to pass a "const char *" when it reads
strings from device tree using of_property_read_string_index().

Change-Id: I98d32524151b2486863e7fd51c56bc8f16262808
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>