soc: qcom: socinfo: Annotate switch cases with fall through

Introduce fall through annotations in the switch statements of
socinfo_debugfs_init() to silence compiler warnings.

Acked-by: Vaishali Thakkar <vaishali.thakkar@linaro.org>
Fixes: 9c84c1e7 ("soc: qcom: socinfo: Expose custom attributes")
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>