iio:kfifo_buf improve error handling in read_first_n.
iio:kfifo_buf improve error handling in read_first_n.

These two elements were originally in the patch
iio:kfifo_buf  Take advantage of the fixed record size used in IIO
but Lars-Peter Clausen pointed out they should not have been
so here they are.

Signed-off-by: Jonathan Cameron <09f65b71b7655725897b2fd41a09a0cefe2e1ace@kernel.org>
Tested-by: Lars-Peter Clausen <3318dc5ce3e4fb7c28a0b841b6801c884e1d0896@metafoo.de>

TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs