AP_AHRS: Fix typos

libraries/AP_AHRS/AP_AHRS_DCM.cpp

@@ -169,7 +169,7 @@ AP_AHRS_DCM::reset(bool recover_eulers)
             // calculate initial roll angle
             roll = atan2f(-initAccVec.y, -initAccVec.z);
         } else {
-            // If we cant use the accel vector, then align flat
+            // If we can't use the accel vector, then align flat
             roll = 0.0f;
             pitch = 0.0f;
         }

libraries/AP_AHRS/AP_AHRS_NavEKF.cpp

@@ -941,7 +941,7 @@ void  AP_AHRS_NavEKF::writeOptFlowMeas(uint8_t &rawFlowQuality, Vector2f &rawFlo
     EKF2.writeOptFlowMeas(rawFlowQuality, rawFlowRates, rawGyroRates, msecFlowMeas);
 }
 
-// inhibit GPS useage
+// inhibit GPS usage
 uint8_t AP_AHRS_NavEKF::setInhibitGPS(void)
 {
     switch (ekf_type()) {

libraries/AP_AHRS/AP_AHRS_NavEKF.h

@@ -145,7 +145,7 @@ public:
     // write optical flow measurements to EKF
     void writeOptFlowMeas(uint8_t &rawFlowQuality, Vector2f &rawFlowRates, Vector2f &rawGyroRates, uint32_t &msecFlowMeas);
 
-    // inibit GPS useage
+    // inibit GPS usage
     uint8_t setInhibitGPS(void);
 
     // get speed limit