PNP: Mark the function pnp_build_option() as static in resource.c

This patch marks the function pnp_build_option() as static in resource.c
because it is not used outside this file.

Thus, it also eliminates the following warning in resource.c:
drivers/pnp/resource.c:34:20: warning: no previous prototype for ‘pnp_build_option’ [-Wmissing-prototypes]
Signed-off-by: NRashika Kheria <rashika.kheria@gmail.com>
Reviewed-by: NJosh Triplett <josh@joshtriplett.org>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/pnp/resource.c

@@ -31,7 +31,7 @@ static int pnp_reserve_mem[16] = {[0 ... 15] = -1 };	/* reserve (don't use) some
  * option registration
  */
 
-struct pnp_option *pnp_build_option(struct pnp_dev *dev, unsigned long type,
+static struct pnp_option *pnp_build_option(struct pnp_dev *dev, unsigned long type,
 				    unsigned int option_flags)
 {
 	struct pnp_option *option;