[review] fix API break in qmi_message_tlv_read_gfloat()

[Aleksander Morgado]

Hey Thomas, Dan and everyone,

See this MR:
https://gitlab.freedesktop.org/mobile-broadband/libqmi/merge_requests/2

In order to fix this issue introduced when modifying the
qmi_message_tlv_read_gfloat() method, which is part of the API.
https://gitlab.freedesktop.org/mobile-broadband/libqmi/issues/1

-- 
Aleksander
https://aleksander.es