target/hexagon: fix some occurrences of -Wshadow=local

target/hexagon: fix some occurrences of -Wshadow=local

Of the changes in this commit, the changes in `HELPER(commit_hvx_stores)()`
are less obvious.  They are required because of some macro invocations like
SCATTER_OP_WRITE_TO_MEM().

e.g.:

    In file included from ../target/hexagon/op_helper.c:31:
    ../target/hexagon/mmvec/macros.h:205:18: error: declaration of ‘i’ shadows a previous local [-Werror=shadow=compatible-local]
      205 |         for (int i = 0; i < sizeof(MMVector); i += sizeof(TYPE)) { \
          |                  ^
    ../target/hexagon/op_helper.c:157:17: note: in expansion of macro ‘SCATTER_OP_WRITE_TO_MEM’
      157 |                 SCATTER_OP_WRITE_TO_MEM(uint16_t);
          |                 ^~~~~~~~~~~~~~~~~~~~~~~
    ../target/hexagon/op_helper.c:135:9: note: shadowed declaration is here
      135 |     int i;
          |         ^
    In file included from ../target/hexagon/op_helper.c:31:
    ../target/hexagon/mmvec/macros.h:204:19: error: declaration of ‘ra’ shadows a previous local [-Werror=shadow=compatible-local]
      204 |         uintptr_t ra = GETPC(); \
          |                   ^~
    ../target/hexagon/op_helper.c:160:17: note: in expansion of macro ‘SCATTER_OP_WRITE_TO_MEM’
      160 |                 SCATTER_OP_WRITE_TO_MEM(uint32_t);
          |                 ^~~~~~~~~~~~~~~~~~~~~~~
    ../target/hexagon/op_helper.c:134:15: note: shadowed declaration is here
      134 |     uintptr_t ra = GETPC();
          |               ^~

Reviewed-by: Matheus Tavares Bernardino <quic_mathbern@quicinc.com>
Signed-off-by: Brian Cain <bcain@quicinc.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-Id: <20231008220945.983643-3-bcain@quicinc.com>