POSIX: ifdef getreg32() calls in mcu_unique_id()

mcu_unique_id() reads registers at an invalid address in non-nuttx builds.
Added ifdef to return a dummy value for non-nuttx builds.

Signed-off-by: Mark Charlebois <charlebm@gmail.com>

src/modules/systemlib/mcu_version.c

@@ -62,9 +62,15 @@
 /** Copy the 96bit MCU Unique ID into the provided pointer */
 void mcu_unique_id(uint32_t *uid_96_bit)
 {
+#ifdef __PX4_NUTTX
 	uid_96_bit[0] = getreg32(UNIQUE_ID);
 	uid_96_bit[1] = getreg32(UNIQUE_ID+4);
 	uid_96_bit[2] = getreg32(UNIQUE_ID+8);
+#else
+	uid_96_bit[0] = 0;
+	uid_96_bit[1] = 1;
+	uid_96_bit[2] = 2;
+#endif
 }
 
 int mcu_version(char* rev, char** revstr)