Sometimes mbr is erroneously recocognised as FAT partion. Due to this the mbr
partition parser is not being called and the partitions on the media are not
detected. This patch should  fix the problem. The checking is done as in the
linux kernel.

I have seen the problem using usb sticks. Although partitioning and formatting
them under linux. The file system type field in the mbr remains there which
causes the wrong detections as FAT32 type and not as mbr.

Signed-off-by: Zahari Doychev <zahari.doychev@linux.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>