iio: mlx90614: #undef field_{get,prep}() before local definition

Prepare for the advent of globally available common field_get() and
field_prep() macros by undefining the symbols before defining local
variants.  This prevents redefinition warnings from the C preprocessor
when introducing the common macros later.

Suggested-by: Yury Norov <yury.norov@gmail.com>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Jonathan Cameron <jonathan.cameron@huawei.com>
Signed-off-by: Yury Norov (NVIDIA) <yury.norov@gmail.com>

Author: geertu

drivers/iio/temperature/mlx90614.c

@@ -69,7 +69,9 @@
 #define MLX90614_CONST_FIR 0x7 /* Fixed value for FIR part of low pass filter */
 
 /* Non-constant mask variant of FIELD_GET() and FIELD_PREP() */
+#undef field_get
 #define field_get(_mask, _reg)	(((_reg) & (_mask)) >> (ffs(_mask) - 1))
+#undef field_prep
 #define field_prep(_mask, _val)	(((_val) << (ffs(_mask) - 1)) & (_mask))
 
 struct mlx_chip_info {