There are a number of problems with cpm_muram_alloc() and its
callers. Most callers assign the return value to some variable and
then use IS_ERR_VALUE to check for allocation failure. However, when
that variable is not sizeof(long), this leads to warnings - and it is
indeed broken to do e.g.

  u32 foo = cpm_muram_alloc();
  if (IS_ERR_VALUE(foo))

on a 64-bit platform, since the condition

  foo >= (unsigned long)-ENOMEM

is tautologically false. There are also callers that ignore the
possibility of error, and then there are those that check for error by
comparing the return value to 0...

One could fix that by changing all callers to store the return value
temporarily in an "unsigned long" and test that. However, use of
IS_ERR_VALUE() is error-prone and should be restricted to things which
are inherently long-sized (stuff in pt_regs etc.). Instead, let's aim
for changing to the standard kernel style

  int foo = cpm_muram_alloc();
  if (foo < 0)
    deal_with_it()
  some->where = foo;

Changing the return type from unsigned long to s32 (aka signed int)
doesn't change the value that gets stored into any of the callers'
variables except if the caller was storing the result in a u64 _and_
the allocation failed, so in itself this patch should be a no-op.

Another problem with cpm_muram_alloc() is that it can certainly
validly return 0 - and except if some cpm_muram_alloc_fixed() call
interferes, the very first cpm_muram_alloc() call will return just
that. But that shows that both ucc_slow_free() and ucc_fast_free() are
buggy, since they assume that a value of 0 means "that field was never
allocated". We'll later change cpm_muram_free() to accept (and ignore)
a negative offset, so callers can use a sentinel of -1 instead of 0
and just unconditionally call cpm_muram_free().
Reviewed-by: Timur Tabi <timur@kernel.org>
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Li Yang <leoyang.li@nxp.com>