package/dosfstools: fix build with musl

package/dosfstools: fix build with musl

Use correct and standard int types.

Fixes:
    http://autobuild.buildroot.org/results/a09/a0923d7f6d4dbae02eba4c5024bbdae3a52aa85a/
    http://autobuild.buildroot.org/results/62b/62b1a71c4fedb6f9209663e7544d7a36fb42c580/
    http://autobuild.buildroot.org/results/e80/e808e692220ced315d30d8ee9c93bdf4a5e32a03/
    http://autobuild.buildroot.org/results/7b7/7b778b7a9ec8c91ec3cea6ee81c6f5c75f0b959a/

[Thomas: update upstream status.]

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>