mtd: fix building with glibc

src/linksys_bootcount.c misses to include stdint.h.
Apparently musl doesn't mind and includes this header by default,
but glibc does not and causes the build to fail.

Signed-off-by: Josua Mayer <josua.mayer97@gmail.com>

package/system/mtd/src/linksys_bootcount.c

@@ -28,6 +28,7 @@
 #include <endian.h>
 #include <string.h>
 #include <errno.h>
+#include <stdint.h>
 
 #include <sys/ioctl.h>
 #include <mtd/mtd-user.h>