ALSA: emu10k1: optimize mask calculation in snd_emu10k1_ptr_read()

Unlike in snd_emu10k1_ptr_write(), we don't need to keep the value's
bits in place, so we can save one shift.

Signed-off-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>
Link: https://lore.kernel.org/r/20230514170323.3408798-4-oswald.buddenhagen@gmx.de


Signed-off-by: Takashi Iwai <tiwai@suse.de>