compute_intercept_slope() is called from calibrate_8960() (in tsens-8960.c)
as compute_intercept_slope(priv, p1, NULL, ONE_PT_CALIB) which lead to null
pointer dereference (if DEBUG or DYNAMIC_DEBUG set).
Fix this bug by adding null pointer check.
Found by Linux Verification Center (linuxtesting.org) with SVACE.
Fixes: dfc1193d4dbd ("thermal/drivers/tsens: Replace custom 8960 apis with generic apis")
Signed-off-by: Aleksandr Mishin <amishin@xxxxxxxxxx>
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