net: hifemac: #undef field_{get, prep}() before 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.

Signed-off-by: Mikhail Kshevetskiy <mikhail.kshevetskiy@iopsys.eu>

drivers/net/hifemac.c

@@ -402,6 +402,7 @@ static void hisi_femac_get_strings(struct udevice *dev, u8 *data)
 }
 
 /* Non-constant mask variant of FIELD_GET/FIELD_PREP */
+#undef field_get
 #define field_get(_mask, _reg) (((_reg) & (_mask)) >> (ffs(_mask) - 1))
 
 static void hisi_femac_get_stats(struct udevice *dev, u64 *data)