iio:pressure: zpa2326: remove redundant "DEBUG" ifdef

The -Wempty-body gcc warning triggers in the newly added zpa2326 driver:

drivers/iio/pressure/zpa2326.c: In function 'zpa2326_dequeue_pressure':
drivers/iio/pressure/zpa2326.c:578:3: error: suggest braces around empty body in an 'if' statement [-Werror=empty-body]

The use of an empty statement behind 'if (...)' is harmless here, but
it shows that the dev_dbg() macro is not used correctly: when the "DEBUG"
macro is not set, dev_dbg() already defaults to a no-operation, though
one that lets the compiler know that the arguments are used, and lets
it check the format string.

Fixing this also simplifies the driver.

Fixes: 03b262f2 ("iio:pressure: initial zpa2326 barometer support")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>