vmmon: fix always_inline attribute usage

Function declared with __attribute__((always_inline)) should also be
declared as inline, otherwise gcc issues a warning "always_inline function
might not be inlinable". It's just cosmetic but getting rid of known
harmless warnings makes it easier to spot actual problems. Use the
__always_inline macro for LinuxDriverSyncReadTSCs() as this is how always
inline functions should be declared in kernel code.

vmmon-only/linux/driver.c

@@ -676,7 +676,7 @@ LinuxDriverReadTSC(void *data,   // OUT: TSC values
  *-----------------------------------------------------------------------------
  */
 
-__attribute__((always_inline)) static Bool
+__always_inline static Bool
 LinuxDriverSyncReadTSCs(uint64 *delta) // OUT: TSC max - TSC min
 {
    TSCDelta tscDelta;