iommu/omap: Fix debug_read_tlb() to use seq_printf()

The debug_read_tlb() uses the sprintf() functions directly on the buffer
allocated by buf = kmalloc(count), without taking into account the size
of the buffer, with the consequence corrupting the heap, depending on
the count requested by the user.

The patch fixes the issue replacing sprintf() by seq_printf().

Signed-off-by: Salva Peiró <speirofr@gmail.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>