Fix get_signal signature mismatch in axe.c

[Jalle19]

Regression from bc1262c0540f86504b9e6fb2bfcee6d8a9493994. Fixes https://github.com/Jalle19/satip-axe/issues/28

/cc @lars18th

[Jalle19]

With this and the previous fix, the latest master once again works on satip-axe:

[Jalle19]

Still need to fix these apparently:

axe.c: In function 'axe_get_signal':
axe.c:719:5: warning: pointer targets in passing argument 3 of 'get_signal' differ in signedness [-Wpointer-sign]
     get_signal(ad, &status, &ber, &strength, &snr, &db);
     ^
axe.c:57:6: note: expected 'uint32_t *' but argument is of type 'int *'
 void get_signal(adapter *ad, int *status, uint32_t *ber, uint16_t *strength, uint16_t *snr, uint16_t *db);
      ^
axe.c:719:5: warning: passing argument 4 of 'get_signal' from incompatible pointer type [enabled by default]
     get_signal(ad, &status, &ber, &strength, &snr, &db);
     ^
axe.c:57:6: note: expected 'uint16_t *' but argument is of type 'int *'
 void get_signal(adapter *ad, int *status, uint32_t *ber, uint16_t *strength, uint16_t *snr, uint16_t *db);
      ^
axe.c:719:5: warning: passing argument 5 of 'get_signal' from incompatible pointer type [enabled by default]
     get_signal(ad, &status, &ber, &strength, &snr, &db);
     ^
axe.c:57:6: note: expected 'uint16_t *' but argument is of type 'int *'
 void get_signal(adapter *ad, int *status, uint32_t *ber, uint16_t *strength, uint16_t *snr, uint16_t *db);
      ^
axe.c:719:5: warning: passing argument 6 of 'get_signal' from incompatible pointer type [enabled by default]
     get_signal(ad, &status, &ber, &strength, &snr, &db);
     ^
axe.c:57:6: note: expected 'uint16_t *' but argument is of type 'int *'
 void get_signal(adapter *ad, int *status, uint32_t *ber, uint16_t *strength, uint16_t *snr, uint16_t *db);