in_atomic() function should not be used inside a driver, and it does not
guarantee atomic context detection. Following the comment from the
kernel source

/*
 * Are we running in atomic context?  WARNING: this macro cannot
 * always detect atomic context; in particular, it cannot know about
 * held spinlocks in non-preemptible kernels.  Thus it should not be
 * used in the general case to determine whether sleeping is possible.
 * Do not use in_atomic() in driver code.
 */
Signed-off-by: Federico Vaga <federico.vaga@cern.ch>