fix the following 'make includecheck' warning:

  arch/arm/plat-stmp3xxx/pinmux.c: linux/sysdev.h is included more than once.
Signed-off-by: Jaswinder Singh Rajput <jaswinderrajput@gmail.com>
Acked-by: dmitry pervushin <dpervushin@embeddedalley.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>