Move #endif to fix PwmOut.h doxygen

Move the #endif up so it does not include the closing bracket of
PwmOut. This allows the doxygen for PwmOut, classmbed_1_1_pwm_out.html,
to build.

Author: c1728p9

drivers/PwmOut.h

@@ -219,8 +219,8 @@ class PwmOut {
 
     pwmout_t _pwm;
     bool _deep_sleep_locked;
-};
 #endif
+};
 
 } // namespace mbed