imx-kobs: fix build for recent toolchains

Starting with Linux 4.4 headers, mtd-user.h isn't including stdint.h any
more which breaks the build.

Fixes:

  http://autobuild.buildroot.net/results/05a/05a159c7f8382237d4c941b1bb6de7dad72708f3/



[Thomas:
 - fix minor typo in the patch description
 - add reference to the autobuilder failure, as suggested by Baruch.]

Signed-off-by: Gary Bisson <gary.bisson@boundarydevices.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>