clk: ralink: mtmips: Fix uninitialized use of ret in mtmips_register_{fixed,factor}_clocks()

Clang warns:

  drivers/clk/ralink/clk-mtmips.c:309:9: error: variable 'ret' is uninitialized when used here [-Werror,-Wuninitialized]
    309 |         return ret;
        |                ^~~
  drivers/clk/ralink/clk-mtmips.c:285:9: note: initialize the variable 'ret' to silence this warning
    285 |         int ret, i;
        |                ^
        |                 = 0
  drivers/clk/ralink/clk-mtmips.c:359:9: error: variable 'ret' is uninitialized when used here [-Werror,-Wuninitialized]
    359 |         return ret;
        |                ^~~
  drivers/clk/ralink/clk-mtmips.c:335:9: note: initialize the variable 'ret' to silence this warning
    335 |         int ret, i;
        |                ^
        |                 = 0
  2 errors generated.

Set ret to the return value of clk_hw_register_fixed_rate() using the
PTR_ERR() macro, which ensures ret is not used uninitialized, clearing
up the warning.

Fixes: 6f3b1558 ("clk: ralink: add clock and reset driver for MTMIPS SoCs")
Closes: https://github.com/ClangBuiltLinux/linux/issues/1879


Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Acked-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>