pw_kvs: Update float test to build for device
pw_kvs: Update float test to build for device

Update test for Put of floating point value to to use float rather than
double to avoid compile warning with [-Werror=float-conversion].

Change-Id: Ifd4b8551cfe30164dc04f23e5fb375c87442185c

google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed