wifi: mt76: Add check for devm_kstrdup()

Add check for the return value of devm_kstrdup() in
mt76_get_of_data_from_mtd() to catch potential exception.

Fixes: e7a6a044 ("mt76: testmode: move mtd part to mt76_dev")
Cc: stable@vger.kernel.org
Signed-off-by: Haoxiang Li <haoxiang_li2024@163.com>
Link: https://patch.msgid.link/20250219033645.2594753-1-haoxiang_li2024@163.com


Signed-off-by: Felix Fietkau <nbd@nbd.name>