i965: Silence warnings about mixing enum and non-enum in conditional

i965: Silence warnings about mixing enum and non-enum in conditional

Reduces my build from 6451 warnings to 6301 warnings by silencing 150
instances of

../../SOURCE/master/src/intel/compiler/brw_inst.h: In function ‘brw_reg_type brw_inst_src1_type(const gen_device_info*, const brw_inst*)’:
../../SOURCE/master/src/intel/compiler/brw_inst.h:802:55: warning: enumeral and non-enumeral type in conditional expression [-Wextra]
    unsigned file = __builtin_strcmp("dst", #reg) == 0 ?                       \
                    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
                    BRW_GENERAL_REGISTER_FILE :                                \
                    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                    brw_inst_##reg##_reg_file(devinfo, inst);                  \
                    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../../SOURCE/master/src/intel/compiler/brw_inst.h:811:1: note: in expansion of macro ‘REG_TYPE’
 REG_TYPE(src1)
 ^~~~~~~~

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Samuel Iglesias Gonsálvez <siglesias@igalia.com>