microblaze: fix custom fprintf

Using GCC-4.2.4-1ubuntu4, there is a warning:
	microblaze-dis.c:792: warning: unused variable 'fprintf'

Indeed, fprintf() is shadowed by a custom redefinition but is not used because
of FORTIFY_SOURCE option which replace calls to fprintf() by fprintf_chk().
So, fprintf refers to the libc implementation instead of the qemu one.
It's a bug.

It is fixed by renaming the variable to something different of "fprintf".
It prevents from hazardous shadowing.

Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>
