drivers/sensor: lsm6dso: Remove busy wait on bank change

It's not necessary to busy wait 150 µs after changing register banks.
Nothing in the data sheet nor app note suggests this.  ST's own HAL,
which is used by this driver, does not delay when changing banks.  It
does a bank change around every function that accesses a non-user bank
register (it's quite inefficient).

So if it was necessary it would be broken now, as most of the bank
changes have no delay.

One of the few page changes that did have this delay are the those done
before and after reading a sensor sample.  Which is where the speed is
significant and is limiting the update rate the driver is capable of.

Signed-off-by: Trent Piepho <trent.piepho@igorinstitute.com>