wifi: mt76: mt7915: fix overflows seen when writing limit attributes

wifi: mt76: mt7915: fix overflows seen when writing limit attributes

DIV_ROUND_CLOSEST() after kstrtoul() results in an overflow if a large
number such as 18446744073709551615 is provided by the user.
Fix it by reordering clamp_val() and DIV_ROUND_CLOSEST() operations.
This commit was inspired by commit: 57ee12b6c514.

Fixes: 02ee68b95d81 ("mt76: mt7915: add control knobs for thermal throttling")
Signed-off-by: xueqin Luo <luoxueqin@kylinos.cn>
Link: https://patch.msgid.link/20241202031917.23741-3-luoxueqin@kylinos.cn
Signed-off-by: Felix Fietkau <nbd@nbd.name>