drm/amd/display: clarify delay param for REG_WAIT

/* macro to poll and wait for a register field to read back given value */

#define REG_WAIT(reg_name, field, val, delay, max_try)	\

#define REG_WAIT(reg_name, field, val, delay_between_poll_us, max_try)	\

		generic_reg_wait(CTX, \

				REG(reg_name), FN(reg_name, field), val,\

				delay, max_try, __func__)

				delay_between_poll_us, max_try, __func__)

/* macro to update (read, modify, write) register fields

 */