recordmcount/MIPS: Fix possible incorrect mcount_loc table entries in modules
On MIPS calls to _mcount in modules generate 2 instructions to load
the _mcount address (and therefore 2 relocations). The mcount_loc
table should only reference the first of these, so the second is
filtered out by checking the relocation offset and ignoring ones that
immediately follow the previous one seen.
However if a module has an _mcount call at offset 0, the second
relocation would not be filtered out due to old_r_offset == 0
being taken to mean that the current relocation is the first one
seen, and both would end up in the mcount_loc table.
This results in ftrace_make_nop() patching both (adjacent)
instructions to branches over the _mcount call sequence like so: