dm table: Remove BUG_ON(in_interrupt())

The BUG_ON(in_interrupt()) in dm_table_event() is a historic leftover from
a rework of the dm table code which changed the calling context.

Issuing a BUG for a wrong calling context is frowned upon and
in_interrupt() is deprecated and only covering parts of the wrong
contexts. The sanity check for the context is covered by
CONFIG_DEBUG_ATOMIC_SLEEP and other debug facilities already.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>