libopenbmc_intf: Fix non-arm devmem implementation

Fixes the following error:

 In file included from button_reset_obj.c:4:0:
 ../libopenbmc_intf/openbmc.h:39:15: error: return type defaults to ‘int’ [-Werror=implicit-int]
 static inline devmem(uint32_t val, uint32_t reg)

Signed-off-by: Joel Stanley <joel@jms.id.au>
diff --git a/libopenbmc_intf/openbmc.h b/libopenbmc_intf/openbmc.h
index c1c0335..fe4deef 100644
--- a/libopenbmc_intf/openbmc.h
+++ b/libopenbmc_intf/openbmc.h
@@ -36,7 +36,7 @@
  //       write_reg(reg,val);
 //}
 #else
-static inline devmem(uint32_t val, uint32_t reg)
+static inline uint32_t devmem(uint32_t val, uint32_t reg)
 {
 }
 static inline uint32_t devmem_read(void* addr)