package/cifs-utils: add upstream patch to fix musl build

Fixes build error with the musl C library:

```
error: '_PATH_MOUNTED' undeclared (first use in this function)
```

Fixes:
http://autobuild.buildroot.net/results/44e/44e800d9933160c48b9c2447d63eeb37a0065d03/
http://autobuild.buildroot.net/results/b9f/b9f918bba4952566e3818fb99f45a7e425acf727/
http://autobuild.buildroot.net/results/8de/8dec8c46ad1959066101efe7cc1781f3d4732028/
http://autobuild.buildroot.net/results/cc3/cc38e7581b4bba362a9be388099b0ea237f4e580/



and many more.

Signed-off-by: Jörg Krause <joerg.krause@embedded.rocks>
Tested-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Acked-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>