soc: qcom: ssr: Correct the returned value of device attribute functions

The value being returned by the SSR store attributes operations
is lesser than the length of the buffer being passed in. As a
result, the operation keeps getting called again in an infinite
loop. Correct this returned value.

Change-Id: I8612b63ee7daae269ca53a4ee9f5213df014b638
Signed-off-by: Deepak Katragadda <dkatraga@codeaurora.org>