Fix FirmwareBootHeaderVerification x86_64 support.

Mount point for block devices is different on x86 and x86_64 devices.
Appropriate check is necessary so proper device can be found.

Checking for "x86" in "x86_64" worked in python but doesn't work in Java.

Bug: 210685521
Fixes: 210685521
Test: FirmwareBootHeaderVerification vts
Change-Id: Id0d8989eacb43065558475f270359a768f7e7f4d
Merged-In: Id0d8989eacb43065558475f270359a768f7e7f4d
(cherry picked from commit 2c6ed869cccf0211dcd2d451bcf1ddf89cb30a75)
1 file changed