drivers: gnss: Correctly set the 1 bit bitfield is_tracked/corrected

Currently, if a SV is tracked, we try to store:
flags & BIT(3) -> 0b1000 -> least significant bit 0 is stored.
Same is valid for the is_corrected field.

Use double negation to treat any non-zero value as true.

Signed-off-by: Philémon Jaermann <p.jaermann@gmail.com>