thermal/drivers/spear: Fix error condition for reading st,thermal-flags

thermal/drivers/spear: Fix error condition for reading st,thermal-flags

of_property_read_u32 returns 0 on success. The current check returns
-EINVAL if the property is read successfully.

Fix the check by removing ! from of_property_read_u32

Fixes: b9c7aff481f1 ("drivers/thermal/spear_thermal.c: add Device Tree probing capability")
Signed-off-by: Gopi Krishna Menon <krishnagopi487@gmail.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@kernel.org>
Suggested-by: Daniel Baluta <daniel.baluta@nxp.com>
Reviewed-by: Lukasz Luba <lukasz.luba@arm.com>
Link: https://patch.msgid.link/20260327090526.59330-1-krishnagopi487@gmail.com